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TRANSCRIPT
Lake Mohegan
Westchester
County
Town of Yorktown
Presentation by Ken Belfer
July 24, 2015
We were # 1 in NYS in 2014
• For the highest BGA counts!!!!
Description of Lake
• Natural Lake
• 103 Acres
• About a mile long
• Much of lake is 12’ deep or less (maximum of 22’)
• Dense residential development around lake
• Municipal storm water systems dump directly into
lake
Lake Conditions
• Low turnover rate
• Eutrophic (rich in nutrients, thus significant growth of rooted aquatic plants and phytoplankton
• High levels of phosphorus in water in summer
• Anoxic conditions exist in deep areas in heat of summer
Background
• Long-time participant in CSLAP
• Also participated in NYS HAB Study (Harmful Algae Blooms)
• Copper sulfate used to treat algae for decades
• Used Alum in 2002 – significant improvement
Watershed
• Relatively small watershed
• 2011 County law banning lawn fertilizer containing phosphorus
• Most of the area sewered in past 25 years
• Expected to see improvement based on these watershed changes
What happened?
• Deterioration in water quality has increased
• In 2013, one test showed phosphorus content of 172 ug/l – NYS guidance value is 20 ug/l
• Stormwater testing in 2013 and 2014 also showed high concentrations of phosphorus in stormwater
Mohegan Lake Improvement District (MLID)
• District created in 1975 after residents petitioned Town of Yorktown
• Special tax district to address Mohegan Lake environment
• Approximately 1500 tax parcels in Yorktown and Cortlandt
• Volunteer board, 3 seasonal staff
• Current annual budget approximately $95,000
Challenges Faced by MLID
• Invasive Species
• Blue Green Algae (cyanobacteria)
• Maintaining suitability of lake for recreational uses (swimming, fishing, boating, picnicking)
Invasive Aquatic Plants
• Eurasian Watermilfoil (myriophyllum) • Was once a dominant plant
• Would make swimming difficult
• Harvesting with weed harvester
leaves fragments, propagating
further spread
• Curly-Leaved Pondweed (potamogeton crispus)
• Has become dominant spring plant in past few years
• Hard to harvest with weed harvester
• Dies off in late June/early July and decays at bottom
Invasive Aquatic Plants
• Water Chestnut (trapa natans)
– Not to be confused with the Chinese vegetable
Invasive Aquatic Plants
• Water Chestnut (trapa natans)
– Can literally cover the lake surface in water less than 6 feet deep, choking out other plant life
– Eradication has been a significant focus for past 6 years
• Initial volunteer effort could not keep up
• Subsequently addressed through weed harvester + hand pulling
Serious Setback
• 2011 – 2012 saw increased public awareness of health risks associated with BGA toxins
• 2012 County Health Dept closed down beaches for season in mid-July due to presence of blue green algae
• 2013 -2014 County mandated beach closures for summer season starting mid-July
• County testing became more sophisticated
– Included identification of algae, and of toxins
Current Activities
• Hand harvesting
water chestnut
• Weed harvesting with
mechanical harvester
– to clear beach areas
– to help clear invasives
– To remove some mass
of nutrients from lake
ecosystem
Current Activities
• Maintaining and expanding aeration system
– 5 sites, multiple compressors and lines
– About 2/3 of lake is covered currently
Current Activities
• Alum
– Submitted permit application to NYS DEC in 2014
– Considering a lobbying strategy
• Copper Sulfate
– Applied for permit in 2015
– County Health Dept closed beaches June 19th
– Allied Biological commenced applications June 23rd
– Applying every two weeks in July and August
– After 2 applications, predominant form of algae in lake was green algae, not blue-green algae
– Beaches reopened June 24th and so far, still open . .
Lake Day July 12, 2015