A concerning new plant on our lakes

Consider the Water Lilies, How They Grow:

SWAN VALLEY - "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.

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 that 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.

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. Swan Valley Connections agreed to help. 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, Sunday, Sept. 9 from 1-5 p.m. at the Holland Lake boat launch. Kayaks and pack rafts would be helpful but anyone who is eager to contribute is welcome. Please contact Rob at SVC rob@svconnections.org; 406-754-3137) to learn more.

 

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