Congress created the San Pedro Riparian National Conservation Area in 1988 to protect a scenic area of southern Arizona.
But a new study by the Center for Biological Diversity says the river still needs protection.
The study says that livestock have damaged 39 of 42 miles of the San Pedro River.
Conservationists have sued the Bureau of Land Management numerous times over the agency's grazing policies, including a recent action over stray cattle.
The damage is significant because the river provides a stopping point for migrating birds.
"The report says that the understory, the vegetation that’s critical for native wildlife along the stream itself is now 93%, 94% gone," said Robin Silver of the Center for Biological Diversity.
He says the BLM has failed to maintain fencing in the area, which the Center addressed earlier this year in a legal complaint.
