Fishponds integrate effects from their catchments and they act like mirrors of the surrounding landscape. Ecological functions of the fishponds and their littorals are strongly subjected by direct or indirect effects of fishery farming and agricultural management in the catchments. Long-term data on water chemistry of the fishponds in the Trebon Basin related to the changes in the fishery and agricultural practices provide an interesting tool for description of important causal relationships. From the 1950s to the end of 1980s, during the period of general intensification both agricultural and fishpond production, the concentrations of main ions and compounds of nitrogen and phosphorus increased considerably in fishpond waters. Data on the water chemistry (35 fishponds sampled 3 tunes a year) and land-use data set gathered during 1990 and 1991 allowed to divide the Trebon fishponds into two following groups. 1) The fishponds with higher conductivity (mean values >350 muS cm(-1)) and concentrations of main ions. These fishponds are located in a close vicinity of farmed agricultural land. Local seepage waters or streams discharging small catchments are main sources of water. 2) The fishponds with lower conductivity, (mean values