were mined. Several smelters operated along Little Cottonwood Creek during the 1870s. Smelting operations produced a variety of by-products that included arsenic, matte, arsenical speiss, and slag. Past mining activities and ore-smelting operations continue to influence the water chemistry of the stream. Mine and smelter tailings in the Little Cottonwood Creek drainage basin can contribute trace metals to the stream. Metals from fluvial tailings deposits in the stream can be re-suspended and dissolved in the stream. Currently, the greatest threat to the streams ecosystem is pesticides from residential run-off. Hydrology The hydrology of the urbanized reach of Little Cottonwood Creek is highly variable and complex because of the canals and diversion structures employed by different water users. Source water for the urban reach of Little Cottonwood Creek varies spatially and seasonally. Sources include snowmelt, stormwater, groundwater, irrigation return, and water imported from the Jordan River. The effect that each of these sources has on stream quality varies seasonally and with stream flow. About 85 percent of the runoff at the mouth of Little Cottonwood Creek was from snowmelt. The hydrology of Little Cottonwood Creek is typical of that of many urban streams along the Wasatch Front and in the Intermountain West. A system of diversions for withdrawal of irrigation water began to be developed on many Wasatch Front streams soon after settlers arrived in Salt Lake Valley in 1847. As the population of the Wasatch Front increased, more of the water in valley streams was needed for drinking and domestic purposes. To meet domestic needs, water is withdrawn from several Wasatch Front streams, including Little Cottonwood Creek, as they emerge from headwater canyons and enter Salt Lake Valley. The water needs of irrigators downstream from the canyon mouths are satisfied with water diverted out of the Jordan River and transported across the valley in a system of canals. Some of the water from the Jordan River is imported to the urbanized reach of Little Cottonwood Creek. The flood stage for the urban waterways is . Notable flooding is rare, with significant flooding in 1983 and as recently as the summer of 2010, when the waterline was above bank level. Fauna The Utah Division of Wildlife Resources stocks the creek with 1,000 trout yearly. The trout are primarily rainbow and Bonneville cutthroat trout. As the higher elevations of the creek still are affected by early mining operations, there is a little