This study aims to determine the diversity of fish at various water levels in Batu Bumbun Reservat, as input material to formulate management activities that must be done to save the reserve. Research was carried out by survey method, in the dry season (April-June) and rainy season (November-December) 2016. Parameters measured, water quality (DO, pH, temperature, TSS, TDS, alkalinity and brightness), fish community structure diversity, uniformity, relative abundance, diversity and dominance),

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... ter levels, and sedimentation. The fish community data obtained were analyzed by the Shannon-Wiener index. The results showed that: (1) Changes in water level resulted in the Batu Bumbun Reservus ecosystem having experienced severe degradation, characterized by fluctuations in water level during two extreme seasons. When the rainy season occurs extreme floods, while the dry season, there is siltation to dry. (2) Community of fish caught in Batu Bumbun Reservus ecosystem of 29 species, consisting of 23 genus and 16 families. When the rainy season is dominantly caught fish community (white fish), with fish density 7.015.000 head / km2, while the dominant season is dominant caught is a community of swamp (black fish), with density of 2,334,000 fish / km2. Based on the analysis of fish community, the value of diversity index (H ') ranged from 1,188-0,825 means low-moderate species diversity, dominance index (C) around 0.0827-0.2147 means no dominant species and uniformity index (E) , 8295-0.6710 means that in a balanced state, there is no competition. It is concluded that the Batu Bumbun Reservus ecosystem has experienced severe degradation, with indicator of fish community change. It is recommended that the management must be done to save the Batu Bumbun Reservus ecosystem is, Dredging, Weed cleaning, Local Fish Restocking, illegal fishing Prevention, Increase of reservat security facility.