A blue-green algae risk advisory previously in effect for Birch Cove Beach at Dartmouth's Lake Banook has been lifted, according to a release Wednesday from the Halifax Regional Municipality. Blue-green algae, or cyanobacteria, occurs in freshwater environments and can multiply rapidly during the summer. Some types of blue-green algae produce toxins during blooms. Toxins may be released into the water when the blooms decay. However, test results showed no toxin-producing blue-green algae in samples collected.