The Role of Predation in Causing Major Changes in the Limnology of a Hyper‐Eutrophic Lake

An experiment was carried out by separation of a shallow man‐made lake into two basins with an earth dam. Unintended leaks allowed extremely fertile river water to feed both basins so that nutrients were unlikely ever to have been limiting to phytoplankton populations. The two basins had greatly differing fish populations. In the basin in which these were low, a chain of events took place in which zooplankton grazing reduced phytoplankton growth sufficiently to allow establishment of aquatic macrophyte populations and an associated diverse benthic invertebrate community. In the basin to which fish had free access from the river, phytoplankton populations remained high, and no aquatic macrophyte community developed. The implications of these observations for shallow lake management are considered.