Montana’s new rules reduce allowable selenium concentrations to 0.8 micrograms per litre of water. B.C.’s current guideline is two micrograms per litre. Montana officials have said those tougher restrictions on selenium are needed to protect waters shared by both countries. Erin Sexton, a senior biologist at the University of Montana, said fish caught in U.S. waters show selenium concentrations high enough to damage their ability to lay eggs and reproduce.