Actual photo. Thats what cyanobacterial blooms look like. Its pretty cool that you can see the flow of water through the baltic - whats not so good is that that algae is going to be taken up by filter feeders, then crabs, then fish and accumulate in the fish we catch as food...not good - but that all depends on the specific species of algae that it is.
Wikis got a couple more pics of similar events...
http://en.wikipedia.org/wiki/Blue-green_algae
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