"Seaweed" is the common name for countless species of marine plants and algae that grow in the ocean as well as in rivers, lakes, and other water bodies.

Michigan has the largest population in the world of starry stonewort, an invasive macroalgae that stifles native plants and fish.  Starry stonewort loves the clean, clear, and calcium carbonate rich waters of Michigan’s inland lakes. It grows in dense mats which can range in thickness from a few inches to a little over six feet. This submerged annual macroalga invades lakes, ponds, reservoirs, and slow moving rivers. It will inhabit freshwater habitats ranging from 3 feet to 95 feet in depth.

Location: Michigan, northern Indiana, southeastern Wisconsin, Minnesota, and the northeast United States

Local Concern: Starry stonewort forms dense mats in lakes and can significantly reduce the diversity of other aquatic plants. Dense mats of vegetation can also impede movement of fish, spawning activity, water flow, and recreational activities.

 Another name for Flatstem Pondweed is Narrow Leaf Pondweed.  Flatstem Pondweed grows completely submerged in the water. Its flat and angled leaves are the first visible and distinct feature. The leaves themselves have one large vein that runs down the middle, with many other smaller veins running in parallel down the length of the leaf. These veins make the leaf more stiff and rigid than other aquatic plant leaves. The only part of the plant that breaks through the surface of the water is the fruit, which looks like a cylindrical spike. 

Location: Northern half of the United States.

Propagation: Seeds and rhizomes. 

Water lilies grow in bodies of water with soil or silt on the bottom. Their large round leaves and solitary flowers float on the surface of the water. The leaves have veins that form a radial pattern and a notch on one side that keeps the leaf from being a complete circle. The flowers can range in color from yellow to pink to white. This plant is not to be confused with Water Hyacinth, which unlike water lilies, has a floating root system and tall purple flowers.

Location: Can grow in all areas of the United States.

Propagation: Produces new plants on the ends of stolons. Can spread very rapidly. 

 Pond scum and seaweed are all examples of algae. Algae are protists with plant-like characteristics, that are typically found in aquatic environments. Like plants, algae  are capable of photosynthesis. Like animals, some algae possess flagella, centrioles, and are capable of feeding on organic material in their habitat. Algae range in size from a single cell to very large multicellular species, and they can live in various environments including salt water, freshwater, wet soil, or on moist rocks. The large algae are generally referred to as simple aquatic plants. Unlike angiosperms and higher plants, algae lack vascular tissue and do not possess roots, stems, leaves, or flowers. 

Water Buttercup has long, branched stems that emerge from both trailing runners and buried rhizomes. The leaves are finely cut into thread-like divisions (white) or flattened divisions (yellow) and either attach directly to the stem or have a very short leaf stalk. Leaves emerge along the stem in an alternate arrangement and are usually stiff enough to hold their shape when lifted out of the water. Water buttercup produces either yellow or white flowers from June to September.

Location: Very common all around the United States.

Propagation: Seed and stem fragments.

 Curly-Leaf Pondweed gets its name from the rippled or wavy nature of its submerged leaves. The leaves are a half inch wide and 2–3 inches long with tiny teeth along the edges. It can grow flowers in the late summer which grow out of the water. Curly-Leaf Pondweed appears reddish–brown in the water but is actually green when observed out of the water.

Location: Commonly found in the Midwest, but is distributed  throughout the entire U.S.

Propagation: Since this species is invasive, avoid transfer of any plant material to other bodies of water.