Based on our own materials, we analyzed the state of the ecosystem of the Suna River in a sluggish flow stretch between two rapids, located within the Kivach Strict Nature Reserve. The taxonomic composition and abundance of zooplankton and zoobenthos were revealed, diversity and saprobity indices were determined. Despite the consequences of economic activity in the form of a layer of bark covering the bottom and a fourfold decrease in the flow volume, the current state of plankton and benthos can be described as stable, similar to that in other rivers in the region. However, an assessment of water quality indicates moderate organic pollution, which makes monitoring necessary.