Temporal analysis of the Hooghly River's water quality: investigating pre- and post-monsoon scenarios in West Bengal, India Open Access

West Bengal's rich geographical diversity spans from the Himalayas to the Bay of Bengal, including the Chhotanagpur Plateau and the Ganga-Brahmaputra Delta. The state's vast river network, led by the Ganga, sustains districts like Hooghly and Murshidabad. Its tributaries are divided into the Upper Ganga Delta rivers, such as Churni and Jalangi, and the flood-prone Lower Ganga Delta rivers, such as Ichamati and Hooghly (Bandyopadhyay et al. 2014). The Hooghly River, also known as the Bhagirathi-Hooghly, weaves a captivating tale as it meanders through the heart of West Bengal, India. Today, the Hooghly remains more than just a waterway – it is a vibrant tapestry of life, sustaining millions of souls along its verdant shores. Studying water quality in the Hooghly River is of paramount importance due to its ecological significance which threatens the delicate balance between nature and human existence, economic, and societal implications. The swift surge in urbanization, agriculture, and related activities has amplified pollution levels in river surface water (Roy & Shamim 2021a; Roy et al. 2022a, b). In West Bengal, river pollution mainly stems from urban and industrial wastewater, with agricultural runoff also contributing, though data is scarce. Many rivers in the area have total coliform (TC) and biological oxygen demand (BOD) levels that surpass safe limits, making them unsuitable for bathing (Das 2018). West Bengal has a complex river network dominated by the Ganga, Brahmaputra, and Subarnarekha basins. While year-round rivers generally face less pollution, dry seasons lead to increased contamination from industrial and municipal sources (Das 2024). Pollution, sedimentation, and encroachment threaten its pristine waters. In pre-monsoon, the Hooghly River seems to hold its breath before the deluge, and its natural resilience masking the creeping threats from industrial effluents, agricultural runoff, and urban waste. In post-monsoon, pollution patterns shift dramatically, especially in urban areas where untreated sewage fuels organic matter and pathogens, causing eutrophication, algal blooms, and oxygen depletion. The river's health ebbs and flows with the seasons, underscoring the urgent need for effective pollution management to safeguard this vital waterway and the diverse communities it sustains. Despite their vital role in sustaining life, rivers face deteriorating water quality due to human activities such as urbanization, industrialization, agriculture, and waste disposal. This poses a serious threat to their sustainability and requires immediate action (Khatoon et al. 2013). The convergence of pilgrimage activities and ferry services along the Hooghly River exerts a significant impact on water pollution levels. The Hooghly River holds spiritual significance, with rituals and ceremonies along its banks emphasizing its sacred properties. During festivals, increased human activity leads to mass bathing and disposal of materials like flowers, food, and ashes, raising organic pollution and microbial contamination. The declining water quality, worsened by urbanization and waste, threatens sustainability and poses serious concerns for the river's future health and the people relying on it. These practices result in heightened levels of organic pollution and microbial contamination in the river (Rai 2013). River water serves various purposes for people, yet continuous urbanization and other irresponsible human activities, coupled with domestic waste, are exacerbating the deterioration of river water quality (Gholami & Srikantaswamy 2009). Water quality relies on various components that must be present at optimal levels to support the healthy growth of aquatic life. Numerous studies conducted across India's rivers consistently depict a concerning pattern of poor water quality and declining aquatic biodiversity (Gupta et al. 2017; Roy & Shamim 2020a, b). Similarly, ferry services add to the pollution burden through the discharge of untreated sewage and waste from onboard facilities. The operation of ferry vessels introduces pollutants such as oil, grease, and detergents into the river, further deteriorating water quality. In urban areas, the ferry service on the river Hooghly, established in 1975 under the authority of the Sundarbans Launch Syndicate, serves as a crucial yet often overlooked mode of urban transport in Kolkata. It facilitates the daily commute of residents between the Howrah and Kolkata banks, as well as transportation between various points along the same bank (Dey 2013). Ferry terminals, docking areas, and pilgrimage ghats contribute to habitat disruption, sedimentation, and water quality degradation in the Hooghly River. This study examines water quality at eight monitoring stations, analysing the relationships among various pollution parameters. Comprehensive pollution mitigation and sustainable management practices are essential to protect this vital resource.

The Ganga, celebrated as India's holiest river, elegantly flows across 26.3% of the nation's landmass and encompasses the largest river basin (CPCB 2013). It is divided into three distinct sections – upper, middle, and lower – the river's significance is immense. Our research focuses on the Hooghly River, a vital distributary of the Ganga, exploring its water quality across both upper and lower stretches in West Bengal. We have carefully chosen eight strategic locations that highlight the river's diverse interactions with human activity, categorized into ferry ghats and pilgrimage ghats (Table 1). The ferry ghats include the bustling Howrah St Ferry Ghat, the vibrant Bally Ghat, Kamarhati Pituri Ghat, Barrackpore Ferry Ghat, and Serampore Ferry Ghat, each reflecting unique local dynamics. In contrast, the pilgrimage ghats encompass the sacred Dakshineswar Temple Ghat, the serene Bag Bazar Mayer Ghat, and the historic B.B. Street Ghat in Uttarpara. This thoughtful selection allows for a comprehensive examination of water quality in both urban and peri-urban environments, shedding light on the critical role of the Hooghly River in the lives of the communities it serves.

In 2022, we undertook the collection of subsurface water samples from these eight carefully chosen locations during both pre-monsoon and post-monsoon seasons. Our analysis encompassed a diverse array of physico-chemical and biological parameters, including temperature, pH, BOD, chemical oxygen demand (COD), dissolved oxygen (DO), TC, alkalinity, hardness, total dissolved solids (TDS), nitrate, nitrite, turbidity, and total phosphorus. This selection of parameters was designed to provide a holistic view of water quality, capturing its dynamic nature and variability across the selected sites.

The selection of parameters was meticulously curated to unveil the river's essence, determining its aptness for human indulgence and domestic embrace. Our endeavour extended to pinpointing the cradle of pollution, nestled within the sacred corners of ferry and pilgrimage ghats, attributing such taint to the relentless dance of humanity. With the elegance befitting an aristocrat, the physico-chemical and biological analyses unfolded, guided by the revered scrolls of APHA (2017). Like a virtuoso's aria, the water quality index (WQI) breathed life into the Hooghly, casting its pristine depths into a symphony of hues, from opulent excellence to a sombre whisper of decline (Roy et al. 2021). And as the moon waxes and wanes, the comprehensive pollution index (CPI) unravelled the river's tales, quantifying its burden with mathematical prowess (Mishra et al. 2016).

In the pre-monsoon season of 2022, water quality (Table 2) parameters along the Hooghly River were assessed against BIS guidelines. The pH map showed seasonal variation, with the river being more alkaline pre-monsoon and slightly alkaline post-monsoon, consistent with (Zafar & Kumari 2024). Lower post-monsoon pH is likely due to increased minerals from soil and rock erosion (Prasad et al. 2020; Kumar & Singh 2021a, b). The pH of water, which indicates hydrogen ion concentration, is key for its suitability for domestic and agricultural use. The ideal pH is around 7.4 (Mondal et al. 2016), but it can vary seasonally and spatially, affecting aquatic life (Goswami et al. 2018). pH levels (6.8–8.18), temperature (29–34 °C), and total hardness (TH) (98–189 mg/L) met BIS standards. Temperature significantly affects the physical, chemical, and biological properties of water, influencing its overall chemistry (Kumari et al. 2013; Raghuvanshi et al. 2014). Most BOD values (2.6–3.4 mg/L) indicated minimal organic pollution, while DO levels (4.98–8.7 mg/L) supported aquatic life. BOD and COD are crucial indicators of surface water pollution (Wang et al. 2018). Surface waters undergo degradation due to both natural processes and human activities, hindering their suitability for drinking, industrial, and agricultural purposes (Singh et al. 2005). DO measures the amount of free oxygen in water, which enters through photosynthesis by aquatic plants and wind-induced aeration. The minimum DO level required for aquatic life is 5 ppm (Das 2020). Lower DO levels can stress aquatic organisms. TDS remained below 500 mg/L, indicating minimal contamination. Ammonia enters aquatic environments through direct sources like municipal wastewater discharge and nitrogenous waste excretion from animals, as well as indirect sources such as nitrogen fixation, atmospheric deposition, and agricultural runoff (Huff et al. 2013). Ammonia levels (0.1–0.45 mg/L) suggested low nutrient enrichment. Although most COD values (10–17 mg/L) complied, elevated counts of TC (110,000–250,000 MPN/100 mL) indicate microbial contamination issues, highlighting areas for pollution management improvement along the Hooghly River. Moreover, nitrate in the Ganges River primarily originates from domestic sewage, industrial effluents, agricultural fertilizers, and aquaculture activities (Sarkar et al. 2007). Deviations from these standards may indicate potential risks to both human health and the environment. Turbidity is caused by suspended particles like clay, silt, organic matter, plankton, and other microscopic organisms in the water (Grobbelaar 2009).

In the post-monsoon season, water quality (Table 3) data along the Hooghly River indicate parameters relevant to surface bathing. pH levels (6.5–8.5) and temperature readings fall within acceptable ranges according to BIS and WHO standards. While hardness levels remain typical for freshwater bodies, elevated BOD levels at certain locations suggest potential organic pollution. Some studies found that water hardness remained moderate year-round (Gray 2014), with hardness found to be 120 and 190, likely due to lower water levels in winter compared with summer and monsoon. DO levels generally support aquatic life but exceed WHO limits at some ferry ghats. Elevated TC counts at specific sites indicate faecal contamination, posing health risks for bathers. Overall, most parameters align with BIS and WHO guidelines, but attention is needed at sites with increased pollution levels to ensure water safety for recreational activities (Table 4).

The correlation coefficient table for the pre-monsoon Hooghly River water quality data reveals significant interactions between parameters, highlighting the impact of ferry ghats and pilgrimage sites. BOD shows strong correlations with TDS and COD, indicating organic pollution from human activities. COD's link with BOD, TDS, and TH suggests substantial organic and chemical pollution. DO, crucial for aquatic life, is significantly affected by BOD, TH, and EC, indicating that organic pollutants and water hardness influence oxygen levels. TDS, indicating dissolved pollutants, correlates with BOD, COD, and EC, reflecting various pollution sources. EC shows significant correlations with TH, BOD, DO, and TDS, emphasizing its role in water quality. Ferry ghats contribute to increased BOD, COD, and TDS due to waste discharge and runoff, depleting DO and affecting TH. Pilgrimage sites cause seasonal pollution spikes, especially during religious events, increasing BOD and COD from waste, which deteriorates water quality and affects DO, TDS, and EC levels. Effective waste management is essential to mitigate these impacts, preserving the river's health and ecological balance.

The correlation table underscores the need for targeted interventions to manage pollution from ferry ghats and pilgrimage activities. The post-monsoon Hooghly River water quality data reveals significant correlations among various parameters, highlighting the impact of ferry ghats and pilgrimage sites. Mass bathing, fuel discharge from ferries, anthropogenic activities, dumping of various ritual items in pilgrimage ghats, deposition of small home idols, flowers, and food, along with grease from ferries, can negatively impact water quality (Roy & Shamim 2020a, b).

The pre- and post-monsoon water quality data for various study area locations along the Hooghly River in West Bengal highlight the influence of ferry services and pilgrimage activities on water quality. Locations experiencing higher ferry service frequencies, such as Howrah St Ferry Ghat and Serampore Ferry Ghat, show elevated levels of parameters like turbidity and TC, possibly due to increased pollution from fuel spills and waste disposal associated with ferry operations, despite having a high frequency of ferry services, showing higher levels of TC, potentially due to offerings and bathing practices. Similarly, pilgrimage activities can contribute to water pollution, as seen in Dakshineshwar Temple Ghat 1. Parameters such as pH, DO, faecal coliform, and turbidity are crucial indicators of water quality, affecting human health, aquatic life, and ecosystem integrity. Deviations from these standards may indicate potential risks to both human health and the environment. This comprehensive examination spanning the pre- and post-monsoon seasons of 2022 paints a vivid picture of the delicate balance between natural processes and human activities along the Hooghly River's sacred shores. This detailed investigation has shed light on the complexities of water quality, revealing the significant impact of human activities, particularly ferry operations and pilgrimage rituals, on the river's ecological health. Throughout the year-long study, findings consistently indicate that the river's waters show clear signs of contamination, largely attributed to the bustling activities along its ghats. Elevated levels of COD and TC counts highlight the pressing need for immediate remedial actions. The sanctity of the Hooghly's waters calls for thorough treatment and purification to ensure that they are safe for use. As we move forward, it is imperative to respond to this call to action with determination, embarking on a path of restoration and renewal. By embracing this challenge with resolve and dedication, we can work towards a future where the Hooghly River flows as a symbol of purity and vitality, exhibiting our unwavering commitment to environmental stewardship and sustainable development. These analyses emphasize the complex interactions between water quality parameters at ferry ghats and pilgrimage ghats along the Hooghly River, underscoring the need for focused monitoring and management strategies tailored to the unique environmental contexts of these sites. This is crucial for preserving water quality and ecosystem health amidst the various human activities and natural forces at play.

We express our deep gratitude to Lt. Dr Misha Roy, Assistant Professor of Environmental Science at Vidyasagar University, for her unwavering support and Prof. Subhas Chandra Santra, Ex-Professor, Department of Environmental Science, University of Kalyani Ex-Coordinator, ENVIS Centre on Environmental Biotechnology (MoEF, Government of India Sponsored) for his invaluable guidance. Additionally, we extend our appreciation to ENVIROCHECK and CONSULTRAIN MANAGEMENT SERVICES laboratories for their meticulous analysis of the water samples, which greatly contributed to the quality and accuracy of this research. We do not like to miss the opportunity to express our gratitude and respect to Professor Joijit Ghosh, Department of English, Vidyasagar University for his support and guidance.

F.S. conceived the concept and performed the field sampling data analyses also worked for interpretation of results and B.C. critically provided feedback and edited the manuscript. Both authors approved the submission of the manuscript. All authors have read and agreed to the published version of the manuscript.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.