Before discussing this season’s treatments, it is very important to understand some history and basic ecology with regards to aquatic vegetation on Geist Reservoir.  Aquatic vegetation is typically beneficial to a waterbody as it provides food for wildlife, fish cover, reduces erosion, and can help filter nutrients and clear the water.  As many of you know, Geist Reservoir has a fantastic fishery that is managed by the Indiana Department of Natural Resources (IDNR), and they set limits on the amount of vegetation that can be controlled.  However, if left unmanaged, dense aquatic vegetation can have negative impacts on navigation, swimming, aesthetics, and can be harmful to fish populations by providing too much cover leading to stunted fish populations.  These problems are often exacerbated by invasive plant species like Eurasian watermilfoil, which resides in Geist Reservoir.  

Prior to 2010, Geist Reservoir had very little submersed plant and filamentous algae growth.  The lake was dominated by planktonic bluegreen algae which led to taste and odor issues as well as toxin production.  In addition, bluegreen algae has very little benefit to fish and wildlife populations, produces surface scums, and severely reduces water clarity.  Not a good condition even though boating was likely much easier at that time!  Around 2010, water clarity increased and bluegreen algae abundance declined.  This was likely due to the introduction of invasive zebra mussels.  This clear water allowed for more plant growth (more sunshine reached deeper in the water).   This plant growth, primarily invasive milfoil, quickly filled in coves and shallow areas of Geist Reservoir with dense surface mats of vegetation.  These dense surface mats covered almost 20% of the lake and severely impacted lake use (see Google Earth images).  Something had to be done on a lake wide level to address this problem.  

In 2013, the Geist Lake Coalition stepped in to manage invasive milfoil by obtaining a small Lake and River Enhancement (LARE) grant for a vegetation survey, vegetation management plan, and treatment.  Following a bid process, Aquatic Control was chosen to complete limited selective invasive milfoil herbicide treatments.  GLC quickly realized that while the treatments reduced milfoil coverage, native vegetation and filamentous algae remained (the LARE program will not fund treatment of native vegetation nor filamentous algae). In 2014, GLC and Aquatic Control met with the Indiana Department of Natural Resources (IDNR) to discuss expanding treatment and allowing for control of native vegetation in certain areas.  IDNR, Indiana Department of Environmental Management (IDEM), and Citizens Energy group permitted native vegetation management in only high use areas of the reservoir with pre-approved EPA registered products (Figure 1). Filamentous algae and selective milfoil treatments were approved along most of the shoreline.  These treatments had to be completed by licensed applicators, who must annually apply for permits.  In addition, permit reports are required to be completed within 7 days of each application.  Treatments needed to be completed frequently throughout the growing season as there is no EPA approved algaecide that can be applied to give long term filamentous algae control (products must breakdown or become inactive shortly after application).  GLC proceeded to raise money and funded maintenance treatments in 2014.  These treatments have continued through present day.  

Figure 1.  Geist Reservoir areas approved for two native plant control application per year.

Figure 1.  Geist Reservoir areas approved for two native plant control application per year.

This year, a total of 183.8 acres was contracted for maintenance treatments by GLC.  In late spring, treatment maps are created by the GLC where residents have donated.  Individual treatment areas are uploaded into a GIS program and transferred onto boat mounted GPS units to ensure accuracy in the application.  Each crew also has individual custom instructions for each area of the lake they manage (174 unique areas are currently being managed).  The treatment plan includes weekly applications starting in late May/early June and ending in late September/early October.  Applications are broken up between four boats that each take care of their 40-50 unique treatment areas.  All the boats are equipped with spray tanks, custom built calibrated spray pumps, and safety equipment.   Some treatment areas are limited by what type of vegetation can be controlled and some areas require special attention as they may be shallower and have more of a propensity towards nuisance growth.  In addition, each applicator must note the type of vegetation in each area for permit reporting purposes.  Algae, if present, is treated every trip, native plants can be treated two times a year where permitted, and invasive milfoil can be selectively controlled at any time of the year.  Plant and algae density varies every year based on water temperature and water clarity, with clarity being the most important factor. 

In 2022, the first treatment was completed on June 2nd.  The water was very clear for late spring and there was more plant growth than the previous few years.  Treatments continued weekly and are still ongoing.  All treatments are completed on Thursdays, except for the June 17th treatment which went down on a Friday to avoid a large bass tournament on the 16th.  Native plant treatments, where allowed, were mostly completed in mid-June and August (applicators are limited to two native plant treatments in approved areas). This treatment timing was designed so that those areas were in good shape for 4th of July and Labor Day.  

Native plant and milfoil growth increased in deeper water this season and reached the surface in many untreated areas by late summer. Typically, the lake would muddy up with the spring rains and not clear until early-summer, but that did not occur in 2022.  Lake users likely noticed plant beds growing much further offshore where they haven’t been in several years.  There have been several blooms of green filamentous algae throughout the season, which is expected.  While this is a very tough algae, applicators can control it within their treatment areas, but this form of algae can float in from untreated zones and returns quickly.  One big problem folks are dealing with now is the abundance of floating plant material.  This material gets chopped up by props and builds up along shore depending on wind direction.  This dead plant material will break down and smell rather bad on hot days.  Native plants, which are rooted to the sediment, have been kept in check where approved, but that is a limited area.  Some treatment areas, where only invasive milfoil can be controlled, are now dominated by native plants.  IDNR has approved several small new zones for native treatment this season as these plants were hindering boat access.  If boat access is not being impacted IDNR will not approve control of native plants in main lake areas.  

A lot of information packed into a few paragraphs!  To summarize, some of the key takeaways are listed below along with a few added bonuses:

  • Plant growth is typically good for a lake as it provides many benefits to the fish, wildlife, and water quality.
  • Treatment of native plant growth is limited by IDNR to high use areas where navigation can be impacted. Treatments are funded outside of these approved zones but are limited to products that only control invasive milfoil and filamentous algae.
  • The amount of plant growth varies every year and is highly dependent on spring water clarity. 
  • Applicators cannot control uprooted floating plants or prevent filamentous algae from moving from an untreated to a treated zone.  
  • IDNR will not approve native plant control unless boat access is being hindered.