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This Symposium emphasized the importance of man-made habitat changes as a major factor which can have an adverse effect on fish stocks. Various impacts were considered, such as lake regulation, land drainage, gravel extraction, and canalisation.
The most common impact of such changes is reduced recruitment, but adverse impacts and migration, food supply and some others were also discussed. The need to pay more attention to gradual cumulative impacts such as those induced by mass outdoor recreation was underlined. To improve forecasting impacts of physical modifications of the habitat on fish and fisheries, the use of Environmental Impact Statements was recommended. The constant need for quantitative data on specific cause and effect relationships was emphasized, so that remedial measures can be clearly outlined at the outset of any activity which will result in a change in river or lake habitat.

The Symposium recommended that, in view of the increasing pressures on fish communities and the quality of fishery resources arising from multiple uses of freshwater ecosystems and associated catchment areas, member countries of EIFAC should give high priority in their research and management programmes to (i) forecasting and monitoring the impact on fish of man-made habitat modifications and of any necessary remedial measures, and (ii) testing and improving existing and new methods of predicting the impact of habitat modifications and of the effectiveness of remedial measures.