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.

The findings have led to an ongoing collaboration with CVRWQCB and with the Nevada County Environmental Health Department. Our findings and our meetings with the county have led to the installation of warning signage by the county, with the possibility of further signage in additional locations as indicated by the data. Based on these levels, the Regional Board has added three of our monitoring sites around the Western Gateway Park swimming hole as Core Sampling Sites for the continuing Safe To Swim Study. We will sample at these three core sites in 2011 from April to September during the peak recreation season. We will sample at five additional stakeholder sites, namely another swimming hole near Western Gateway Park and four sites upstream on Squirrel and Clear Creeks. Sampling upstream sampling of the park will help us to identify and remediate the sources of the contamination. Further collaborations have begun with the Natural Resources Conservation Service and the Nevada County Agricultural Commissioner, who are key partners in working with landowners to implement modifications to their land use practices aimed at protecting the creek from bacterial contamination. We have applied for further funding for education and outreach to stakeholders in the community, and for speciation efforts to pinpoint the sources.