The Tennessee legislature is poised to pass a bill Thursday that, with a last minute amendment, would allow many livestock farms to operate without state water quality permits.

It would exempt all but the largest farms which produce manure and other liquid waste from mandatory permits; medium-sized farms could voluntarily apply for permits. Poultry farms with dry waste, no matter their size, would be exempt.

Industry representatives praised the bill — a modification of a measure passed last year — for eliminating cumbersome regulations, while environmentalists worry that some farmers could cut corners and spill waste into streams and rivers. The agricultural industry, which accounts for 10 percent of the state’s economy, is the leading contributor of water pollution in Tennessee and in the United States.