Aquatic Plant Identification Manual for Washington's Freshwater Plants

Freshwater aquatic plants are found in most lakes and rivers in Washington. They range from tiny floating plants that can form mats on a lake surface to reed-like plants that grow two meters above the water. Aquatic plants are an important part of freshwater environments. They provide food and shelter for a wide variety of insects, amphibians, fish, reptiles, mammals, and birds. They also form an important link in nutrient cycles, and they stabilize shorelines.

How to use this guide to identify plants

We designed this guide for people who do not have a scientific background, but it may also be useful for professionals who need assistance in identifying aquatic species. We do not include all the aquatic plants in Washington. Use additional references if you can’t find a plant here.

Plants with similar growth forms and from similar habitat types are grouped together in categories and each category is identified with an icon. The plant categories in this guide are:

• Shoreline plants

• Floating leaved, rooted plants

• Floating mat, rooted plants

• Free-floating plants

• Submersed plants

• Plant-like algae

• Aquatic moss

• Curiosities

Go to the category that best seems to describe the unknown plant. Compare the plant with the illustrations and photographs of each plant within the category. When you find a similar looking plant, read the species description to see if your plant fits the description. Refer to the Glossary for definitions of unfamiliar terms. See a sample page and a description of the layout of the page. 

If the plant fits the general description, use a metric ruler to measure leaves, petals, and other plant parts.  Sometimes, the number of leaflets or petals helps with identification. When counting the numbers of leaves, especially those arranged in a whorl around the stem, it is often helpful to examine a cross-section of the plant at a node. Use magnification to see the small details of the plant structure.

If the plant doesn’t seem to be referenced within a particular category, look at the plants in similar categories. Depending on the time of year, flowers, fruits, or floating leaves may not be present or underwater leaves may have decomposed. A young plant may appear quite different in appearance than a mature plant.  Don’t be discouraged if you can’t identify the plant to species. Some species, such as the narrow-leaved pondweeds are notoriously difficult to distinguish from each other.

Other icons

If the plant being described is a sensitive, threatened, and endangered species, a non-native invasive aquatic plant, or was used by Native Americans, an appropriate icon will be displayed on the plant description page.

Other references

If you can’t identify the plant from our reference, you may need to consult other plant references. See the references section for a list of publications about aquatic plants.

If you need more help to identify an aquatic plant, check with the our Aquatic weed control technical assistance plant specialist, the local county Washington State University Cooperative Extension Service, the local office of the United States Department of Agriculture, the Natural Resources Conservation Service, the State Noxious Weed Control Board, or your local County Noxious Weed Control Board. Check their online resources or see if they may have staff who could help identify the plant.

• Native Plants for Aquatic Gardens and Aquariums (PDF) is a WSU publication that shows a variety of native water plants.

• Weed Search can help you find a plant.

• Washington Invasive Species Education

• National Invasive Species Information Center Washington State Resources

Return to the the Aquatic Plant Manual home page.