Theodore Roosevelt Lake, a warm monomictic reservoir on the Salt River and Tonto Creek in central Arizona, is chemically influenced more by the Salt River than by Tonto Creek. Roosevelt Lake begins thermal stratification in February and becomes strongly stratified by April. Overall, Roosevelt Lake is considered to be mesotrophic. However, chlorophyll-a concentrations ranged from 0.70 to 14 micrograms per liter, with a mean concentration of 2.8 micrograms per liter, indicating oligotrophy. The Secchi-disc depth ranged from 1.1 to 3.0 meters, with a mean Secchi-depth measurement of 1.9 meters, indicating eutrophy. Mean concentrations of dissolved arsenic, iron, manganese, nickel, and strontium were greater in the streams than in the lake. Mean concentrations of dissolved copper and zinc were greater in the lake than in the streams. Ground water in parts of the Pinal Creek basin contains elevation concentrations of manganese, copper, and other metals and contributes to the flow of Pinal Creek, which is a tributary of the Salt River. Of the lake sites, the forebay had the greatest mean concentrations of dissolved arsenic, iron, manganese, and zinc. In the lake, mean concentrations of chromium, copper, nickel, and zinc in bottom sediment were greatest for the Tonto arm. Median concentrations of chromium and nickel in bottom sediment were greatest for the forebay. Median concentrations of zinc in bottom sediment were greatest at the forebay and Tonto arm. The median concentration of copper in bottom sediment was greatest for the Salt bay.