Consider the Water Lilies, How They Grow

A Concerning New Plant on our Lakes

By Rob Rich
August 31, 2018

“This is where the water lily was last year,” sighed Fish Biologist Beth Gardner, pointing to a small cove in Holland Lake's south shore. The water lily. Singular. Today, water lilies abound there, in a growing patch the size of a Chevrolet Suburban. And there are other patches around the lake's edge, wherever the water is shallow and still. Granted, Beth may have missed a plant or two last year, or mistaken it pre-flower for our native yellow pond lily. But this year, in shock at the profusion of white, she had one of those moments with a gulp and the thought: I don't think I've seen that before.

SVC Conservation Director Luke Lamar looks down upon a pioneering water lily just starting to spread – by seed and root – in a Holland Lake cove.
Photo: Rob Rich

Though relatively new to Montana, neighbors ranging from the Pacific Coast to Seeley Lake know the fragrant water lily (Nymphaea odorata) well, and most are not fans. Believed to be introduced from its native range (in the eastern United States) for the horticultural intrigue of Seattle's 1909 Alaska-Yukon-Pacific Exposition, the plant has since spread throughout the West. It is currently listed as a noxious weed in Washington State, and its habit of monopolizing water surfaces is cause for concern regionwide. No part of the plant is toxic, but its thick, leathery pads block out the light, which in the short-term protects and feeds the amphibians, fish, and aquatic insects who lurk among the stems. But over time, the lilies become photosynthetic traps, hoarding so much sun they trigger a cascade of interacting effects that reduce the diversity of other submerged plants, increase water temperatures, thwart winds dispersing the lake's plankton, and more. The clear, nutrient-poor lakes of northwest Montana are ill-adapted to these rapid and substantial changes in summer, but also in winter, when the lilies' mass decay reduces oxygen for native creatures under ice.

Closing at night and opening by day, the fragrant water lilies’ flowers are well-named, smelling something like vanilla with hints of chamomile. After a summer of gobbling up space on the water’s surface, the large, Pac-Man-shaped leaves begin to lose chlorophyll and sink to decay underwater.
Photo: Rob Rich

The water lilies' effects touch people too, as any boater, swimmer, or fisherman who's gotten snarled among them could say. The question, as each new invasive asks in its own way, is what to do? Within a week of discovery, the Forest Service, whose jurisdiction includes Holland Lake, determined this was a prime case for early detection and rapid response, the preventive mantra of invasive species management. SVC agreed to help, and last week we partnered to learn the best methods for treatment, which currently includes aggressive removal of flowers to thwart seed production, and pads/stems to starve the plant's photosynthetic capacity. Unearthing the entire root would be ideal, but at some depths, scuba gear would be required. Or beavers, who consume the roots as food in quantities that help manage plant populations in the East, as described in Hope Ryden's classic Lily Pond. But for now, with repeat cuttings over the next few years, SVC and the USFS hopes to make an old phrase true, nipping it in the bud.

We invite volunteers to help us monitor and manage this plant, especially for our second water lily pull, on Sunday, September 9 from 1-5pm at the Holland Lake boat launch. Kayaks and packrafts would be helpful, but anyone who is eager to contribute is welcome. Please RSVP & contact Rob at SVC (rob@svconnections.org; 406-754-3137) to learn more.

Seven people. About 200 pounds of water lilies pads, flowers, and stems. Please help us beat that on September 9!
Photo: Beth Gardner