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2 CURRENT KNOWLEDGE 1. Blue Cypress Lake has been recognized as relatively pristine as shown by the fact the FDEP identified it as a reference lake used to develop state water quality standards. 2. Blue Cypress Lake and its connecting waterbodies are Class 1 waters designated for potable water use. 3. A sustained upward trend in total phosphorus in Blue Cypress Lake began in .approximately 2006 and is not accompanied by upward total nitrogen trends. Since 2014 the upward trend has accelerated. 4. The major processes that deliver phosphorus to the lake include surface runoff, groundwater, point source discharges to the lake, and internal loading. 5. Agriculture is the primary land use and has remained relatively constant for several decades in the Blue Cypress Lake watershed. 6. The use of fertilizers, and more recently biosolids, are the most likely of sources of phosphorus delivered to the lake by these processes. 7. Application of Class B biosolids began in 2006 in the Blue Cypress Lake watershed based on the agronomic needs of nitrogen for hay production. Pressley Ranch biosolids applications began in 2013. 8. Point sources are less than 1 percent of the total phosphorus load to Blue Cypress La ke 9. Water chemistry, in particular dissolved oxygen, was relatively constant before and during the sustained upward trend, suggesting that the internal loading from sediments is unlikely. 3 ANALYSIS RESULTS 10. Tributary water quality data representing the three major surface water sources to Blue Cypress Lake do not show the upward trend in total phosphorus. 11.A phosphorus budget for Blue Cypress Lake based on measured incoming TP concentrations shows and modeled hydrologic fluxes indicates that prior to 2013 the inputs exceeded the outputs from the lake. Since 2013, more phosphorus began leaving the lake then entering the lake which indicates an unaccounted-for source of phosphorus since 2013 source. 12. Beginning in 2013 the annual TP application rate downstream of the water quality sampling stations averaged approximately 200,000 pounds per year (Ib/year). That difference means that if only 10 percent of the phosphorus in those biosolids reaches the lake, it would account for all the unaccounted-for phosphorus. 13. Class B biosolids applications in the Blue Cypress Lake watershed are based on the agronomic needs of nitrogen for hay production with an assumption based on site- specific testing that phosphorus could generally be taken up by the crop and retained by the soils. The resulting phosphorus loading averages close to 10 times the agronomic needs. 4 ONGOING DATA COLLECTION 14.The site-specific testing for phosphorus capacity (Mehlic-1) was not done using the method now recommended and used by IFAS in Florida (Mehlic-3). 15. Phosphorus Capacity Index results from 11/6/2018 on the Pressley Ranch biosolids application sites show that the 19 of the 23 sites exceed the phosphorus threshold 142