Tomblin advised residents Thursday not to drink, bathe or cook in the water and to only use it for flushing.
The declaration involves the counties of Kanawha, Boone, Jackson, Lincoln and Putnam.
Officials are not sure what threat the chemical spill poses to humans.
Media outlets report the chemical leaked from a tank at Freedom Industries and overran a containment area on Thursday. The amount that spilled isn't immediately known. A chemical smell was in the air.
Department of Environmental Protection spokesman Tom Aluise says the chemical is used in the coal preparation process.
Freedom Industries did not immediately respond for comment.