Lake monitoring surveys data are vital and have been being accumulated for every lake. However data itself, without effective data management and interpretation, cannot be used to tell the story or history of the lake. Therefore, this project aims to develop a new water quality database system for a lake with systematical functions to utilize such data effectively and to satisfy both general public users and specialists. Lake Biwa was chosen as the target lake, where long-term monitoring data were available for almost one hundred years. A relational database application, Access 2002, with the help of Macro functions and VBA (Visual Basic for Applications) was introduced to organize all of the data. With the systematical storing of data, valuable data could be easily accessed, filtered and powerfully utilized for researchers own interests. The filtered data can be written into basic documents (spreadsheet or text files), provided for outside requests, and again used for further basic and advanced analysis by a reading back process. The system supports multiple users, especially public users by providing user interface system and visualized result displays. The final outcomes from this systematic data utilization can be fruitfully used as the guideline for effective monitoring management program of lake water quality.