Manitoba will tighten rules on expanding hog farms and ban manure spreading to cut the flow of phosphorus into the world’s 11th-biggest freshwater lake, as Lake Winnipeg deteriorates from algae growth.

The western Canadian province, which has the country’s third-largest pig herd, will also protect wetlands that filter out pollutants and force the capital Winnipeg to build a sewage treatment plant, Premier Greg Selinger said on Thursday.

The buildup of nutrients like phosphorus from sewage, farms or natural sources is a major environmental problem for the world’s lakes and rivers, including Lake Winnipeg.

It causes growth of blue-green algae that can produce toxins that sicken humans and animals, and use up the water’s oxygen. “The objective is to save the lake from going dead on us,” Selinger told reporters.

Canada is the world’s third-biggest shipper of pork. But changes in Manitoba are not likely to impact markets because hog production has been falling for several years in the province.