BAYKALSK, Russia — Toilets are the talk of Lake Baikal these days, at least among the ecologically minded.

For years, their main bogyman was the Soviet-era Baykalsk Paper and Pulp Mill that sat on the shoreline belching pollutants into the spectacular lake, which contains about one-fifth of the unfrozen freshwater on the earth’s surface. Three years after the plant closed, the fight to preserve the lake has shifted to different battlegrounds.

Some consider the next struggle even harder. It involves changing the daily habits of people who have lived in this distant corner of Siberia for generations, as well as controlling the waxing tide of mostly Chinese tourists for whom the lake has become a romantic destination.

“It was easy to say this plant is to blame, it is bad,” said Marina Rikhvanova, 55, who made preserving the lake her lifelong ambition. “It is much harder to say that I am to blame because my toilet is the problem.”