Duckweed are round and oval like free floating leaf bodies on the water's surface, which can be found either individually floating or found conglomerated in clusters. Duckweed tends to be more prevelant near inflows and wind protected areas. The plant itself is very small (about 1/16th of an inch) with 1-3 leaves grouped together with a small hair like root.
In small amounts and with careful management duckweed can be beneficial for pond health; however it can and completely cover a ponds surface quickly. This causes changes in water temperature and light penetration to the bottom of the pond which may cause further issues. Duckweed can also be very difficult to control once a large population is established.
Watermeal is a very small (smaller than duckweed) green free floating plant. A grain of watermeal is less than 1mm in size and have no root systems to hold them in place. When it begins to grow it tends to come in thick colonies along with duckweed and it can become an aggressive invader of a pond.
Watermeal tends to grown and excel in areas with calm water and minimal wake; the plant itself is very easily transmittable across water bodies. Like Duckweed, Watermeal can cover the entire surface of the pond causing issues with light penetration and temperature. Once populations have been established, Watermeal can be difficult to remove.