Results of previous studies. In 1997, Ecology published a TMDL evaluation report about the lower Yakima River (Joy and Xxxxxxxxx 1997). The Environmental Protection Agency (EPA) approved the TMDL for the protection of chronic aquatic life criteria in 1998. The report details the amount and sources of several pollutants in the lower Yakima River. The TMDL noted that the relationship between turbidity, suspended sediment, and DDT would likely change significantly after most of the suspended sediment was removed from the river. Therefore, the TMDL intended to identify specific human health load allocations for DDT starting in 2007. In addition to those TMDLs, temperature monitoring is performed at two lower mainstem Yakima River locations, the Prosser xxxx and the Xxxxx xxxx. Those gages are operated by the USGS and the U.S. Bureau of Reclamation. Temperature data from other locations and for shorter periods of record are also available from a number of sources. There has not been a TMDL drafted for temperature in the lower Yakima River. In 2011, Xxxxxx Conservation District (BCD) summarized two years of temperature monitoring and habitat assessment in the Assessment of the Lower Yakima River in Xxxxxx County, Washington (Xxxxx et al. 2011). Xxxxx summarized the conclusion of thermal profiling as follows (p. 96): With temperatures well above 21°C for the 2008 and 2009 summer floats mainstem Lower Yakima River temperatures were inhospitable for salmon as expected; however, temperature heterogeneity within the lower Yakima River was identified. Although a predominantly [losing] reach, localized areas of cooler temperatures were identified. These “cooler” areas were the result of: a) non- point source seeps that are likely discharge points for shallow groundwater seeps fed by irrigation and river recharge, b) irrigation wasteways (e.g., Spring and Xxxxxx Wasteways, Corral Creek Wasteway, and Amon Creek Wasteway) c) and “holes” (e.g., tail of oxbow at Xxxxxx Ranch). The “cooler” areas are located along the riparian area and in some instances behind side channels (e.g., island at I-182 bridge).
Results of previous studies. Data from water quality monitoring in the lake from past efforts have pointed to two key sources of phosphorus contributions to the lake: surface inflows during winter months, and internal loading due to hypolimnetic anoxia that promotes dissolved phosphorus release from the lake sediments In the last several decades there have been numerous studies and plans focusing on Lake Xxxxx, Lakewood Park, and the Salmon Creek Basin (Table 1). Table 1: Studies and Plans with a focus water quality in Lake Xxxxx and the surrounding watershed.
