Swartswood State Park consists of Big Swartswood Lake (Big Lake) and Little Swartswood Lake (Little Lake). Big lake is 519 acres while Little lake is 84 acres. A two-year stocking program was initiated by Swartswood State Park and the Swartswood Lake and Watershed Association during the summer of 1999. Big Lake was stocked with weevils in 1999 and 2000, while Little Lake was stocked in 1999 only.
Little Lake received 15,000 weevils in three areas in June of 1999. Weevil damage was observed at all stocking sites during the follow-up surveys in August of 1999. EWM plants were no longer flowering, and Coontail had replaced much of the EWM as the dominant plant. The results of the monitoring sites data also indicated the EWM plants had collapsed out of the water column and were no longer flowering. In some monitoring and stocking sites Chara, American Pondweed, and Coontail were observed during follow-up surveys and not during initial surveys. This indicating that EWM decline is allowing native species to rebound and balance the ecology of the lake.
Big Lake received 12,000 weevils in two areas in July of 1999. At the time of the first follow-up survey, ten weeks post-stocking, the severity of weevil damage was striking in both stocked sites. Damage was the most severe in the middle of the beds and decreased at the edges of the bed. Weevil eggs were found on several stems, and little to no flowering was occurring.
Big Lake received an additional 15,000 weevils in five areas in July of 2000. Weevils were found in three newly established 2000 stocking sites, indicating that the weevils had spread to EWM infested areas not originally stocked in July 1999. Much of the EWM in the 1999 stocking sites was already damaged at the time of the initial survey (prior to the 2000 stocking) and numerous adults were observed on the healthy meristems present in the bed. The weevils stocked in 1999 overwintered successfully and returned to the plant bed. Weevil eggs and larvae were found in all stocking and monitoring sites at the time of the 2000 follow-up survey. Weevil damage was extensive in all stocking and monitoring sites. The number of native plants encountered in the transects, increased over the course of the project and in several of the sites the native species were nearly as dense as the EWM.
Little Lake did not receive additional stocking during the 2000 season. The results from the second year's follow-up survey indicate weevil density increased in all stocking and monitoring sites except for one. Weevils and extensive damage were found in all sites. Several of the plant beds were not topped out as extensively as during the summer of 1999. The number of native plant species observed increased from 1999 to 2000 and three new species were noted in 2000. In total, the number of native species in Little Lake samples increased from two to six.
The stocking event of 1999 and 2000 in Big and Little Swartswood Lakes resulted in heavy damage to all EWM beds in both lakes indicating the MiddFoil® Process has been a success. The weevil population has increased and appears to be thriving. The increase in native aquatic plants over the course of the two year study should increase the likelihood of a continued EWM decline as they continue to compete with the milfoil for light and nutrients.
