Mesotrophic lakes are standing water bodies with a surface area greater than 1 ha, which have moderate levels of alkalinity and nutrients. Although they may look similar to other standing water types, this is an unusual loch type in Britain. The sites have clear water and support a wide range of species. Mesotrophic lakes occur relatively infrequently, but this category includes several important sites which support rare species, such as slender naiad Najas flexilis. These sites are also often good fishing lochs.