Okay but what is the impact of not opening it?

Pretty sure it's bad either way.

Two environmental groups are threatening Monday to file suit against the Army Corps of Engineers, the Mississippi River Commission and the Interior Department for failing to evaluate the impact of repeatedly opening the Bonnet Carre Spillway.

They cited the spillway's effects on nine endangered species, including sea turtles, birds, fish and marine mammals.

The threat to sue, issued Monday, is required by federal law to be delivered to federal agencies 60 days before a lawsuit is to be filed. The law gives the agencies time to correct any legal wrongdoing they may have committed before the suit is filed.

Meanwhile, it's high river season already.