Flowering Rush: An invasive aquatic problem

A light wind blew across the top of Flathead Lake causing small ripples to move blades of an aquatic plant that many residents along the shorelines of the lake have taken concern with. 

Members of the Flathead Lakers, a non-profit grassroots group dedicated to keeping a clean watershed in the Flathead Lake area, gathered to listen to Peter Rice, an ecologist from the University of Montana discuss the work he is doing to try and combat the further growth of this insidious weed.  

Flowering rush, an invasive weed originating in Eastern Europe, moved its way in to American waterways in the 1890s when it was introduced to the St. Lawrence River system. It was first found in Flathead Lake in 1964 in Peaceful Bay. 

The plant looks very similar to sedge, an aquatic grass looking plant, making it easy to look over and not think too much about. But, according to Rice, there are some serious issues that are being presented with the proliferation of the plant. 

Flowering rush has the capability to choke out water systems as it builds up the bottom with its heavy organic material as well as its ability to collect sediments as they slowly move past the plant. It also collects algae on the leaves that stand above the water, giving the Great Pond Snail, the pesky little creature that is well-known for carrying the swimmers itch parasite, a great place to eat and live as well as giving the invasive Northern Pike a premium place to lay its eggs, further allowing the fish to be in heavy competition with the native Bull Trout and Western Slope Cutthroat Trouts. 

“It’s an example of how one impact can change the whole ecology of the lake,” Rice said. 

Rice is working with the Tribes to find ways of eliminating the plant without serious ecological damage in the process. Currently, Rice and his colleagues are observing patches of lake bottom they sprayed with an herbicide called Habitat to see how it works against the flowering rush. In April, they sprayed the test areas with the herbicide and the patches, which can be seen off the western side of Ducharme access, are still weed-free. Whether or not this means that the weed won’t move back in is still in the air. “I wouldn’t say we’ve come close to eradication,” said Rice. 

Flowering rush is able to move across the lake bottom via a root-like system called rhizomes. The rhizomes grow from one end and spread the plant across areas as deep as 22 feet. The rhizomes can also be spread when waterfowl, people, or boats shake up the bottom and ride on currents or waves until they settle, starting the growth over again in a new location. 

The plant’s prime growing areas tend to be in slow moving water and grow well along shorelines and shallow ponds. As of 2006, there were well over 2,000 acres that are affected by flowering rush with the potential of over 14,000 acres being taken over by the plant. 

Testing of the herbicide, Habitat, is still ongoing in the Ducharme Fishing Access area and the plots where it has been applied can be seen off the west of the fishing access point.