1. The possible impacts of abstraction of water from streams and rivers in the UK have generated concern in conservation bodies.
2. This paper examines the feasibility of using biotic scores and predictions from the computer-based RIVPACS system to assess the effects of abstractions on benthic fauna.
3. Control and impacted sites on 22 rivers which experienced abstractions for hydroelectric power generation, supply of drinking water (either directly or through groundwater abstraction), spray irrigation and fish farming, were examined.
4. The ratios of observed to predicted biotic scores and comparison of observed fauna with that predicted by RIVPACS were used to assess the biological quality of the sites.
5. Only 11 of the 51 sites on the 22 rivers showed signs of reduced environmental quality. These included eight sites on a small lowland stream which receives run-off from fertilized agricultural land and is subject to spray irrigation; two sites on upland streams which had experienced severe spates prior to our survey and a small chalk stream, the Pang.
6. Discharge, baseflow, substrate and altitude were factors which explained most of the variation in faunal parameters such as biotic score, numbers of species, numbers of families and total abundance.
7. The main conclusions of the study are that upland streams did not appear to suffer adverse effects as a result of abstraction whereas lowland streams appeared to be more degraded, but with the exception of the Pang this could not necessarily be attributed to abstraction.
8. Biotic scores with RIVPACS cannot be used to set minimum ecological flows but can be used either directly, to assess site-quality and to identify areas of concern which may or may not be related to abstraction; or indirectly, by reference to the RIVPACS data-base to assess the conservation interest of invertebrate assemblages.