The enantiomer fractions (EFs) of alpha‐hexachlorocyclohexane (α‐HCH), cis‐, trans‐, and oxychlordane, and heptachlor epoxide were measured in 73 snow, fish, and sediment samples collected from remote lake catchments, over a wide range of latitudes, in seven western U.S. National Parks/Preserves to investigate their sources, fate, accumulation and biotransformation in these ecosystems. The present study is novel because these lakes had no inflow or outflow, and the measurement of chiral organochlorine pesticides (OCPs) EFs in snowpack from these lake catchments provided a better understanding of the OCP sources in the western United States, whereas their measurement in fish and sediment provided a better understanding of their biotic transformations within the lake catchments. Nonracemic α‐HCH was measured in seasonal snowpack collected from continental U.S. National Parks, and racemic α‐HCH was measured in seasonal snowpack collected from the Alaskan parks, suggesting the influence of regional sources to the continental U.S. parks and long‐range sources to the Alaskan parks. The α‐HCH EFs measured in trout collected from the lake catchments were similar to the α‐HCH EFs measured in seasonal snowpack collected from the same lake catchments, suggesting that these fish did not biotransform α‐HCH enantioselectively. Racemic cis‐chlordane was measured in seasonal snowpack and sediment collected from Sequoia, indicating that it had not undergone significant enantioselective biotransformation in urban soils since its use as a termiticide in the surrounding urban areas. However, nonracemic cis‐chlordane was measured in seasonal snowpack and sediments from the Rocky Mountains, suggesting that cis‐chlordane does undergo enantioselective biotransformation in agricultural soils. The trout from these lakes showed preferential biotransformation of the (+)‐enantiomer of cis‐chlordane and the (−)‐enantiomer of trans‐chlordane. Environ. Toxicol. Chem. 2011; 30:1533–1538. © 2011 SETAC