Acidic

Acidity is measured using the pH scale. A score of 1 is very acid - 7 is neutral - 14 is alkaline. Water flowing over or through rocks like limestone and chalk tend to become slightly alkaline. The rivers of West Yorkshire, however, start their life in the acidic conditions of the moorland peat. They then flow over gritstones, sandstones and shales. As a result they are acidic in nature. This adversely affects levels of fish living in the rivers.