Restoration and maintenance of native macrophytes in lakes – partnership with Riley Purgatory Bluff Creek Watershed

Project manager: Ray Newman

Native aquatic plants provide critical fish and invertebrate habitat, stabilize sediment, and help maintain water clarity in lakes. However, invasive aquatic plants reduce populations of both fish and native plants, and create undesirable conditions for recreational users. Therefore, the restoration of native vegetation is an important management goal.

Additionally, in many shallow lake systems, the presence of benthic fish (such as common carp) uproot native plants, stir up sediment, and release nutrients – all of which result in poor water quality and the loss of submersed vegetation. Therefore it is also valuable to reduce the abundance of common carp when working to improve water quality. The rapid recovery of native plant communities after fish removal requires an integration of several strategies.

Phase I description:

This project focuses on the Riley Purgatory Bluff Creek Watershed, which includes Lakes Riley, Susan, Ann, Staring, and others. Please click here for a map.

In 2009, as part of another MAISRC project, Developing and implementing a sustainable program to control common carp, 80% of the common carp in Lake Susan were removed, and water quality improved. However, invasive plant populations became more abundant and a broader project to restore the native plant community was initiated. Surveys indicated that milfoil weevil densities were high enough to control Eurasian watermilfoil. Endothall treatments were conducted in 2013 and 2014, which successfully controlled curly-leaf pondweed. To enhance the native plant community, native plants from nearby Lake Ann were transplanted in 2009, 2010, and 2011. These transplants were found to be successful, especially with water stargrass, wild celery, and bushy pondweed. Overall, the plant community is expanding and improving in Lake Susan, but some water quality concerns remain.

Carp were also removed from Lake Riley in 2009. Eurasian watermilfoil increased after the removal, likely because the high population of sunfish kept the milfoil weevil population too low to effectively control the plants. By 2012, curlyleaf pondweed was also expanding. Therefore, a lakewide treatment for curlyleaf pondweed was implemented in 2013 and 2014 which was effective. Eurasian watermilfoil biomass, however, continued to increase.

In nearby Lake Staring, carp were removed as part of a separate effort in 2012, 2013, and 2014, but researchers are still working to remove them to target levels. Eurasian watermilfoil is not present in this lake and as carp populations decrease, researchers will use strategies developed in Lakes Susan and Riley to enhance native plant populations and control invasives such as curlyleaf pondweed.

Project start date: 2009

Project end date: 2014

Progress and updates:

MAISRC graduate student thesis examines effect of herbicides on curlyleaf pondweed and native plants (MAISRC Newsletter)


Phase II description:

In addition to Lakes Susan, Riley, and Staring, which were studied in Phase I, Phase II of this project includes Lake Lucy and Lake Mitchell. The specific objectives are to:

  1. Continue efforts to restore native plants and control invasives in Lakes Riley, Susan, and Staring.
  2. Assess early season herbicide treatments to control curlyleaf pondweed in Riley, Susan, and possibly Mitchell, and assess possible combination treatments to control Eurasian watermilfoil in Lake Riley.
  3. Assess milfoil weevil populations in Lakes Riley and Susan, with a focus on sustaining biological control of Eurasian watermilfoil in Lake Susan and an assessment of feasibility of biological control in Riley.
  4. Recommend and assess further approaches to enhance establishment and growth of native macrophytes while controlling or preventing development of nuisance populations of curlyleaf pondweed and Eurasian watermilfoil, including the use of alum treatments to improve water clarity in Riley and Susan.
  5. Apply these approaches in Lake Staring as necessary to restore native aquatic plant communities, including transplanting native plants and/or applying herbicide treatments.

Project start date: 2015

Project end date: 2017

Progress and updates:

MAISRC researchers examining effects of alum treatments on curly-leaf pondweed and native plants (MAISRC Newsletter)

Expanding research capacity for aquatic invasive plants (newsletter article)