Sierra Streams/FODC has conducted three duplicate studies with the Central Valley Regional Water Quality Control Board (CVRWQCB), in September 2008, June 2009, and September 2010, as part of the Regional Board's Safe to Swim study. The studies confirmed levels far in excess of the EPA safe limit of 235MPN/100ml for a single grab sample. From April 22 to May 20 2009, SSI/FODC collected five samples to determine the geometric mean, found to be 320-353 MPN/100ml. The geometric mean safe level is 126 MPN/100ml. At the "safe" level, the EPA predicts a total of 8 sicknesses per 1000 exposed people. The range of values from samples collected in spring and summer of 2009 has been 42–1300MPN/100ml in the swimming hole itself, and even higher upstream in the two creeks that flow into the park. EPA studies have shown a high probability that swimmers are routinely sickened at these levels, and in all likelihood do not connect their illness with their exposure from swimming in the creek. In September 2010, samples were collected throughout the month of September, with 63% exceeding the single sample maximum, offering further evidence that contamination persists throughout the recreational swimming season.