The Bonneville Power Administration last week announced rate increases for both wholesale power and transmission costs that will go into effect Oct. 1.

The Flathead Electric Cooperative had already increased rates for its customers in anticipation of the higher costs from its main power supplier. Co-op customers saw a 3.75 percent increase last month and can expect a 3 to 3.5 percent increase in June 2014.

The Co-op’s board of trustees chose to raise its rates incrementally to help smooth the transition for its customers to higher power costs. Last month’s rate increase cost less than $4.75 per month for most residential Co-op customers. General manager Ken Sugden said about half the Co-op’s expenditures go to paying BPA for power.

BPA announced July 24 that its wholesale power rate would increase an average of 9 percent to cover higher costs for maintaining and operating the federal hydroelectric system, higher costs for fish and wildlife mitigation programs and reduced revenues from sales of surplus power due to low market prices.

The agency also announced an 11 percent increase in its transmission rate, the first increase in this rate in six years. The increase will help pay for replacing and repairing the BPA’s aging infrastructure and for mandatory compliance and security requirements.

BPA’s final rate proposal will be filed with the Federal Energy Regulatory Commission at the end of July for a 60-day public review and approval.