Use crayfish to keep Hampstead Heath swimmers at bay | Brief letters

Protect wildlife ponds | Champions League final | Avoiding Arsenal | Colonial attitudes | Nine times tableI know how to stop swimmers using the wildlife ponds on Hampstead Heath (Report, 27 May). Erect a picture of all the enormous crayfish – an invasive species – now inhabiting many of the ponds, particularly the one pictured. I certainly wouldn’t want to be swimming with them snapping at my toes.Emilia Benjamin
London• A cup final between clubs from London and Paris (Par