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September 19, 2011 TO: Members of the GLWMO Board of Commissioners FROM: Tom Petersen Administrator SUBJECT: Highlights/Paraphrase summary of the April, 2009 Barr Lake Owasso Use Attainability Analysis Report Overview: Study provides the scientific foundation for a lake specific management plan. Study completed in 2007 and 2008. Very dry years. Additional stormwater monitoring completed in 2009. Citizens have concerns about excessive macrophytes that competes with recreational uses and decreasing lake clarity. Conclusions: • Water quality data from 2007 & 2008 would classify Owasso as an Eutrophic Lake. • Data from 1998 to 2008 shows decrease in Secchi Disk with little change in Phosphorous and increase Chlorophyll a. • Owasso's water quality falls within expected range for a minimally- impacted lake with similar characteristics and shows potential for water quality improvement. • There is internal loading within Owasso but may be significantly less than the average observed across the Metro area. • May 2007 survey shows Curlyleaf pondweed on 52% of the Lake and can act as a significant source of phosphorous (2010 study which was conducted after the LOA sprayed for vegetation showed Curlyleaf pondweed on 17% of Lake). • Evidence suggests the lake stratifies in the summer. • It is possible for mixing to occur in shallow areas of the Lake as the result of wind and motor boat activity although it is unclear what role mixing has on the overall water quality of the Lake. Anecdotal information suggests that turbidity in the Lake increases as the result of motor boats in shallow areas of the Lake. • Carp may be a problem in the Lake resulting in internal phosphorous release and loading. • Watershed runoff plays a variable roll in total phosphorous loads to the Lake depending on climatic conditions ranging from 12 to 23% of the total load. • Internal phosphorous loads from within the Lake (the result of Curlyleaf Pondweed die -back, release from Lake sediments, wind mixing, and rough fish activity were estimated to range from 50 to 57% of the Load to the Lake. Other sources include atmospheric deposition and groundwater. • In Lake Monitor modeling indicates that control of Curlyleaf Pondweed will have the most significant impact on total phosphorous concentrations.