Bear Lake

An economic gem worth protecting

The Bear Lake Eurasian watermilfoil project is an excellent example of adaptive management, quick learning, and cooperation between multiple agencies. This project has been different from our other projects because Eurasian watermilfoil (Myriophyllum spicatum) is currently not listed as a noxious weed in Utah. However, it is listed in 3 of our surrounding states, including Idaho, which shares half of Bear Lake with Utah. Because of the potential impacts, we approached the plant like an EDRR species and prioritized mapping, planning and rapid treatment. Currently, this species has been recommended for listing in Utah by the State Weed Committee.

This project has been a huge collaboration between Matt Coombs (Project Manager) and team from Forestry, Fire, and State Lands (FFSL), Jeremey Varley and team from Idaho State Department of Agriculture (ISDA), and the Utah Department of Agriculture and Food (UDAF).


Why worry about it

This project was located on the Utah side of Bear Lake in Rich County. Bear Lake is known for its clear blue water and is a very popular spot for recreation. Additionally, Bear Lake provides important habitat for fish, including 4 endemic fish. It is a part of the Bear River watershed, which is a large source of water for northern Utah and the Great Salt Lake. There are a lot people and agencies working together to ensure the health of Bear Lake and the Bear River watershed. Because this lake is high up in the watershed and is a popular recreation site, the chances of Eurasian watermilfoil spreading not only downstream and to other locations on recreational vehicles are high.

Due to its placement high in the watershed, the chances of Eurasian watermilfoil spreading on recreation vehicles is HIGH.


Invasiveness of Noxious Weeds

Eurasian watermilfoil (Myriophyllum spicatum) is a submerged aquatic plant that is native to Eurasia. It is a perennial plant that spreads through seeds, plant parts, and rhizomes/stolons. Spreading through plant parts from auto-fragmentation and plant damage are thought to be the primary means of spread. In the United States, this plant has exhibited many invasive qualities that include forming monocultures, outcompeting native plants, decreasing habitat for fish and birds, decreasing water oxygen levels, and inhibiting recreation. Additionally, when the plant dies back in the fall, it releases nitrogen and phosphorus into the water. This nutrient loading could eventually increase the risk of toxic algal blooms.

photo by: Robert L. Johnson, Cornell University, Bugwood.org

Project Location

Bear Lake is located on the Utah/Idaho border, north of the town of Logan, approximately 145 miles northeast of Salt Lake City.

We conducted the project treatments at:

  • Swan Creek
  • Camp Hunt
  • Daisy Bay
  • Azure Cove Marina
  • Ideal Beach
  • Rendezvous Beach


Treatment

Based on the advice of Idaho State Department of Agriculture (ISDA) and the overwhelming benefits of ProcellaCOR EC, FFSL choose to use this herbicide to use. Also, based on the advice of ISDA, they applied the herbicide when Eurasian watermilfoil was almost fully grown, but before the plant was flowering. They sprayed 46.7 acres on July 27th, 2020. The amount of herbicide used depended on both the area and the depth of water. After spraying, they dredged some of the smaller populations, but it was very labor intensive and difficult to do in deeper water.

Many more populations of Eurasian watermilfoil were found after the treatment in 2020. As a result, they decided to spray later in the season in 2021 to ensure that no populations were missed. Also, due to drought in 2021, many of the sites that were sprayed in 2020 were no longer under water in 2021. As a result, they were able to use cheaper chemicals on these exposed sites including Polaris (Imazapyr) and Roundup Custom.

Due to drought in 2021, many of the sites that were sprayed in 2020 were no longer under water.


What we did

We went out on June 24th-26th, 2020 with a large team of kayakers and a boat to conduct fine scale monitoring on populations. FFSL used the data from this monitoring to create precise polygons for the herbicide treatments to minimize any herbicide impact and waste.

If the population was smaller than 0.5 acres, it was slated for mechanical pulling. Populations that were larger than 0.5 acres were sprayed.

After treatment, we resampled the same grid, but only within the treatment polygons on August 31st through September 1st, 2020. Since September 2020, FFSL has continued mapping and treating, and they have found populations in areas we had previously mapped as negative for Eurasian watermilfoil. If these are new populations, the rate of spread of this plant is alarming. We revisited the same polygons and sampled along the same grid on August 30th–31st , 2020.


Results

Swan Creek Marina

North of State Park Marina

State Park Marina

Daisy Bay

Azure Cove Marina

Ideal Beach

The Point Marina

Epic RV

Rendezvous Beach


Results

After completing our coarse mapping, we estimated a total cover of about 7% on the west side, including Rendezvous Beach. The east side had much less Eurasian watermilfoil with about 2% cover. On the west side, the biggest populations were found in marinas and on the south sides of the marinas, except for Rendezvous Beach. This could possibly indicate that the plant populations establish best in slower moving water or possibly a pref- erence for certain soil types. This is also concerning because it will be likely that the plant will be spread by boats leaving the marina to other parts of the lake. Therefore this is where most of the treatments occurred in 2020. On the east side of the lake, there are not as many marinas and the littoral zone is shorter, so the patterns were not as clear. For post treatment, we also recorded if the plant was damaged by the herbicide or not. Damage could include the leaves turning yellow or brown, the apical meristem flattening, the connective tissue swelling, the tips of the plants curling, or the plant dying and turning to black mush. The degree of damage was not recorded. To calculate this, we took the total number of rakes with damaged Eurasian watermilfoil and divided by the total number of rakes with any Eurasian watermilfoil and multiplied by 100. This gave us the estimated percent of plant damage.

When looking at marina vs. open water, the cover was higher on average in the marinas in 2019 and 2020. Additionally, the herbicide seemed to be slightly more effective in the marina verses the open water because there was more plant damage in the marinas then in the open water. It seemed like we were pulling out more dead mush or at least browning leaves in the marinas. Where in the open water areas, the damage seemed to be much less (e.g. the leaves were starting to yellow). In 2021, we observed the effect of the herbicide more clearly as the total cover in marinas dropped while the total cover increased in the open water areas.

Stages of Eurasian watermilfoil


Conclusion

This project is an excellent example of multi-agency cooperation even across state borders.

Additionally, it is a great example of early detection and rapid response. A coarse mapping of Eurasian watermilfoil populations across the whole lake, multiple sessions of detailed motoring, and two rounds of treatment have been completed. This has been a huge learning experience for all of us here in Utah, and FFSL has done an excellent job at quickly adapting new methods and adjusting them as needed. Eurasian watermilfoil is spreading throughout the lake, but the total cover is fairly low and predominantly in the marinas and silty areas. The occurrence of missed/new populations form 2019 to 2020 is concerning and indicates the need for quick and effective control. ProcellaCOR EC seems to be impacting the species and causing damage. The drought in 2021 provided us with an alternate way of treating Eurasian watermilfoil, and we are looking forward to observing the effectiveness of the treatment.

Project summary for 2021

Project photos

Project Partners

UDAF funds projects on a SIIPA score method

To learn more please visit https://utahweedsupervisors.com

Utah Department of Agriculture

Aaron Eagar

Mapping and reporting

photo by: Robert L. Johnson, Cornell University, Bugwood.org

Stages of Eurasian watermilfoil

Project summary for 2021