because the aire flows through the former industrial landscape of west yorkshire, it was heavily polluted. in 2007, yorkshire water carried out improvements to esholt sewage works at a cost of £110 million under the eu's fresh water fish directive. whilst trout are prevalent above keighley, the river is host to others such as chub, dace, barbel & grayling, whilst sea trout have been noted as far upriver as shipley. work is also being undertaken to make some weirs easier for fish to negotiate. improvements have allowed otters and european water voles to return to the river as the water and food quality is far superior to that when the river was polluted. in the upper reaches of the river around bell busk and malham, white-clawed crayfish are present in the tributaries.