The multivariate analyses gave a much clearer picture of the influence of environmental variables on invertebrate assemblages than the LQI index. All three types of analysis showed that periods of drought play a more important part in assemblage composition than years with regular rainfall. The TWINSPAN analysis to Level 5 generally grouped the sites according to flow rate and bed type. Indicators were quite common families, but
separated according to their substrate preference. The DECORANA analysis grouped sites according to whether the water was held back by mills and locks, or flowed freely under bridges and over weirs. In 1997, the drought year, these groups were indistinct