Wetlands in the plains, when full of water, cover up to a sixth of the land area. Wetlands are high in biological diversity, and support a wide variety of native plants and animals, which are adapted to the fluctuating water levels. Due to the variable water levels, shallow wetlands were drained and others made deeper and more permanent. This has altered wetland ecology and reduced habitat for many species. Species have difficultly in travelling from one habitat to another, as the distances are further. As a result, gene pools are isolated and species are threatened.