New approaches and tools, including appropriate technical guidance documents, are needed to facilitate ecosystem analyses of watersheds as required by the Clean Water Act. In particular, there is a pressing need for refinement and release of an ecological risk methodology that addresses the direct, indirect, and synergistic effects of nutrients, metals, toxic organic chemicals, and non-chemical stressors on aquatic ecosystems, including streams, rivers, lakes and estuaries. The ecosystem model AQUATOX is one of the few general ecological risk models that represents the combined environmental fate and effects of toxic chemicals. The model also represents conventional pollutants, such as nutrients and sediments, and considers several trophic levels, including attached and planktonic algae, submerged aquatic vegetation, several types of invertebrates, and several types of fish. It has been implemented for streams, small rivers, ponds, lakes, and reservoirs. AQUATOX Release 2 is described in these documents. Volume 1: User's Manual describes the usage of the model. Because the model is menu-driven and runs under Microsoft Windows on microcomputers, it is user-friendly and little guidance is required.

"EPA 823-R-04-001 [v.1]; EPA 823-R-04-002 [v.2]; EPA 823-R-04-003 [v.3]." "January 2004."

v. 1 User's manual.-- v. 2 Technical documentation.-- v. 3 User's manual for the BASINS (version 3.1) extension to AQUATOX release 2.