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Lake Fukami-ike is a small eutrophic lake, to improve the water quality of the lake, a lakemanagement project was carried out in 1992. This project involved nutrient diversion and revetmentconstruction along the lake shore. A biotope was built near the lake in 2000. As a result, although the inorganicnitrogen in the lake decreased considerably, chlorophyll-a (phytoplankton) increased slightly. The zooplanktoncommunity in the lake before the project in 1978-1979 predominantly comprised large-sized species (about 1.8mm), however, small-sized species (about 0.1-0.2 mm) were dominant after in 2013-2015. The reason for thedecrease of the large-sized zooplankton was thought to be the possibility of losing habitat space because aquaticmacrophytes of the littoral zone were filled up when revetment construction built in 1992. We compared thebody length and composition of zooplankton community between the lake (nearly emergent plants on the lakeshore) and the biotope (emergent and floating-leaved plant cover). Large-sized zooplankton (about 0.9-1.2mm) were dominant in the biotope, and size distribution did not differ in 1978-1979. The presence of developedaquatic macrophytes was suggested to promote the survival of large zooplankton.

Lake Fukami-ike is a small monomictic and eutrophic lake, located in southern Nagano Prefecture in Central Japan. An uncommon phenomenon of dissolved oxygen 0-1 mgL -1 from the surface to the bottom layer occurred on 16 November, 2013. On November 2, Trichocerca similis (Rotatoria) etc. dominantly distributed from 0-5 m depth depending on distribution DO concentration. Tintinnopsis lacustris (Protozoa) was found in the bottom layer (anoxic condition). The number of cells (Fragilaria rumpens (Bacillariophyceae) etc. abounded from the 0-5 m layer. On November 16, T. lacustris distributed from the surface to the bottom layer. Then, T. lacustris continued to distribute from the surface to the bottom layer, and the genus Synedra was found to have distributed uniformly from the surface to 6 m depth in the next investigation on 21 December, when the DO concentration was about 10 mgL -1 from the surface to the bottom layer. The changes in vertical distribution of T. lacustris, seemed to indicate that lake water was lifted from the bottom layer when shift stagnation periods to circulation periods.

Lake Fukami-ike is a small monomictic and eutrophic lake, located in southern NaganoPrefecture in central Japan. Water quality improvement was expected from maintenance of farm villagedrainage and waterfront function was carried out for town activation in 1992. However, no blue-green algalbloom outbreak had occurred before. We studied the water quality and compositions of the zooplankton andphytoplankton before and after building a bulkhead maintenance construction. Large decreased values forNO3-N, NH4-N and NO2-N were 1.87→0.50 gNm-2(26.7%), 1.49→0.78 gNm-2(52.3%) and 0.085→0.030gNm-2(35.3%), respectively. Aphanizomenon flos-aquae (Cyanophyceae) were dominant in the summer;some species of the genus Fragilaria were dominant among phytoplankton during study periods. Thedominant species of zooplankton during study periods were Keratella cochlearis (Rotatoria); smaller thanCyclops vicinus (Crustaceae) were dominant species of zooplankton before the construction.