In cold climates at high latitudes or altitudes, the surfaces of both small streams and large rivers freeze in winter. In winter, the layer of surface ice reduces nutrient inputs and light penetration, limiting the productivity of these ecosystems and the diversity of their biota. In spring, meltwaters transport increased organic matter and nutrients, producing seasonal peaks in abundance of algae and phytoplankton. Animals, such as fish and beavers, tolerate near-freezing water temperatures, while a range of invertebrates and other vertebrates come to forage from spring to autumn.