The definitions of TMDL-related terms presented here are intended to provide the reader with a working knowledge of terms that apply to Virginia's TMDL program. This is the first in a series of Virginia Cooperative Extension publications that deal specifically with TMDLs. The federal Clean Water Act requires States to develop TMDLs for streams, rivers, lakes and estuaries that do not or are not expected to meet applicable water quality standards. This glossary is designed to assist the reader in understanding and interpreting TMDL related information that may come from sources as varied as governmental agencies, environmental groups, consulting firms, or the news media.