Fragrant Water Lily – September 2020 Weed of the Month

Fragrant water lily (Nymphaea odorata) has many redeeming qualities as well as causing significant problems here in Washington. This species of water lily is native to the eastern and central United States and is used both by people and wildlife, but it is not native to Washington. It is appreciated for its beautiful, lotus-like, sweet-smelling flowers that attract both people and pollinators. It was that beauty that attracted people to this plant and inspired them to use it in water gardens starting in the early 1800’s. It comes as no surprise that it has been very popular in our area as well. Over the years, it has been introduced to countless lakes and ponds in western Washington, as well as spreading to new water bodies on its own, carried by currents and wildlife.

fragrant water lily leaves and flower
Fragrant water lily (Nymphaea odorata) was introduced into the Pacific Northwest for its lovely blossoms but has become invasive. Photo by Katie Messick.

Unfortunately, this hardy water lily thrives in our climate and in our lakes to the point where it creates extensive, dense populations that can be detrimental to people and the environment. A small amount of water lily on lakes and ponds can be beneficial, in the same way as our native lake plants such as yellow pond lily (spatterdock), watershield, and pondweeds. However, fragrant water lily grows much more densely and into deeper water than our native floating-leaved plants.

dense growth of fragrant water lily
Fragrant water lily grows in deeper water than most of our native lake plants, creating solid carpets of leaves and dense underwater stems. In this photo, native spatterdock grows in a narrow band near the shore and the non-native water lily extends far out into the lake. Photo by Ben Peterson.

The large, dense fragrant water lily mats can be a hazard to swimmers and boaters as well as creating stagnant, low-oxygen and high temperature areas that are harmful to fish. In the fall, when the extensive mats of leaves decay, this can increase algae problems and lower water quality, as well as being unpleasant for lake users.

fragrant water lily plants on a lake
Fragrant water lily grows so densely that it interferes with recreation such as boating and swimming and degrades fish and wildlife habitat in lakes. Photo by Beth LeDeux.

Fragrant water lily forms huge, interesting looking rhizomes that grow in the lake bottom and help this plant survive year after year. When fragments break off, they are carried by water currents and create more populations around the water body. Water lily also forms seeds that move in water currents and that are also eaten by ducks, which carry them to new water bodies.

fragrant water lily rhizomes
Fragrant water lily has large rhizomes growing in the lake bottom and when pieces break off, the plant spreads in the water current. Photo by Katie Messick.

One of the fascinating things about fragrant water lily is how it produces seeds. Each flower is open for only three days. On the first day, it is receptive to pollen and forms a liquid in the flower, which insects fall into, washing off the pollen and sometimes trapping the insect. On the second and third days, the flower produces pollen and no liquid so insects can carry the pollen away to other flowers. After the three days, the flower closes and the stem coils up, pulling the flower down into the water, where the seeds mature. Plants continue to produce flowers all summer like this, producing a steady supply of lovely blooms and numerous seeds.

Fragrant water lily blossoms
Fragrant water lily blossoms for many months but each flower is only open for a few days. Photo by Beth leDeux.

Despite the pretty flowers, lakeside property owners often regret planting fragrant water lily and soon work hard to get rid of them. In large lakes, this can be a huge challenge and can be cost-prohibitive to undertake for most landowners and public agencies. However, in small lakes it is not nearly as difficult. Small populations of water lily can be cleared by simply removing the top growth as it appears over several years. If this is done consistently, especially before the growth reaches the water surface, it can eradicate a small population in two to three years without having to dig up the massive rhizomes.

cut fragrant water lily stems
Fragrant water lily can be cut repeatedly to keep it controlled around a dock. Photo by Holly D’Annunzio.
dock with cleared area around it
Keeping a clear route around your dock is possible with regular cutting. Photo by Holly D’Annunzio.

However, even this simple control method requires that you obtain the Aquatic Plants and Fish pamphlet from the Washington Department of Fish and Wildlife (publication #APF-1-98) and follow its instructions. This pamphlet is the HPA permit that is required for manual control of aquatic noxious weeds in Washington. Other methods including chemical control are also effective, but will require additional permits and licenses, and will likely involve hiring a licensed contractor to perform the work.

Portage Bay’s water lily problems are too large to tackle by hand. Photo by Ben Peterson.
fragrant water lily showing one area treated and one area not treated
Large infestations of fragrant water lily are best tackled by a professional aquatic contractor who has the equipment and expertise, not to mention the right permit and license. In this photo, the area on the right was treated by a licensed contractor. Photo by Ben Peterson.

More information can be found in King County’s Best Management Practices for Fragrant Water Lily and on our fragrant water lily page. Also, see our blog post on where to go for help with aquatic weed control for information about permits and other requirements when working in the water. For a few inspiring stories about people working together to control water lily and other lake weeds, see our blog post about lake residents teaming up to tackle weeds.

people standing by a large pile of fragrant water lily
Lake residents teamed up to remove huge amounts of fragrant water lily growing around their lakeshore. Photo by Holly D’Annunzio.

Because fragrant water lily is not regulated (meaning control is not required) in King County and is very widespread, we are not tracking locations at this time. However, we can provide technical assistance on this noxious weed and any others, so please feel free to contact us if you have any questions or visit our website for more resources and information on noxious weeds.

Fragrant water lily leaves seen from under water
Fragrant water lily leaves seen from under water.
fragrant water lily leaves and two flowers
Fragrant water lily leaves are round and notched and the flowers are usually white, fragrant, and lotus-like.
fragrant water lily on a lake
Given the chance, fragrant water lily can cover huge areas of our lakes like here on Cottage Lake. Photo by Sasha Shaw.