A second batch of birds were released Wednesday after being cleaned of a mysterious goo.
The goo, described as a gummy substance, has affected more than 500 birds in the San Francisco Bay area.
International Bird Rescue says about 20-to-30 rehabilitated birds were released along the East San Francisco Bay in Oakland. Another 81 birds were previously released.
The organization said Wednesday that 323 birds were brought to them for cleaning. The species include Surf Scoters, Horned Grebes, Common Goldeneyes and Scaups.
About 170 birds died after getting covered in the odorless substance, which sapped the seabirds' ability to insulate themselves against the cold.
California state investigators have not determined the source or what was in the mystery goo.
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