Azolla, Mosquito Fern
Mosquito fern floats on the surface, forming large colonies, and can be green or red to brown.
Mosquito fern is a free-floating plant that grows in still waters, slow-moving waters, or resting on mud. The leaves are oppositely arranged around the stem. There are two lobes: one floating and one below the water’s surface. Leaves are green when actively growing and red to brown when stressed. Mosquito fern is often found mixed with duckweed and/or watermeal. It can cover the whole pond quickly, blocking out sunlight and oxygen (leading to fish kills).
Mosquito fern can be found in much of the United States: northeast, southeast, south, and midwest.