Human impact on ocean life

I have chosen the topic of the human impact on ocean life for my research paper. I had been thinking of writing on this topic for quite some time. However, when I saw the recent news about the millions of dead fish that appeared (seemingly over night) in a west coast harbor. I find it very disturbing that things like this are happening. I to take a little bit of comfort in the fact that the city is trying to find ways to use these dead fish rather than just disposing of them in the trash. I read an article today that said officials were allowing local community members to come pick up some of the fish to use as fertalizer in their yards and gardens. Some of the other fish were being transported to an organic composting site. . As the clean up in the California harbor continues, fears are now turning to possible bacteria pollutants in the air and water from decomposing fish. Some areas of the harbor floor are up to three feet deep in dead fish. Low oxygen levels in the water is said to be the cause of this massive kill-off. I can't help but wonder what on earth caused the oxygen levels in the water to drop so rapidly.