When I saw the title of this submission, the free-association part of my brain immediately said "algal bloom". On thinking about it a little more, it became obvious that this was a more apt comparison than I realized... but first, some background:
Algae grows in water with relatively high amounts of dissolved nutrients (phosphates and nitrates). As it grows, it uses oxygen, since it's a single-celled plant. An algal bloom occurs when a sudden large source of waterborne nutrients enters the ecosystem (like raw sewage). When this happens, the growth of the algae takes off- and since it's single-celled, it grows faster than anything else in the habitat. This means that it uses up all of the available oxygen and suffocates the fish and plants.... For this reason, it's the bane of aquarium keepers, water treatment plant workers, and ecologists everywhere. There are regulations on the amount of nutrients that may be present in otherwise clean water that is released from a sewage treatment plant expressly for preventing algal blooms which can sterilize a river.
I'm not old enough to remember the time before the September that never ended, but I do remember a lot less spam and a lot less in the way of general email obnoxiousness when I got my first nonshared email account, just three years ago... and in light of that, the algal bloom analogy is more apt that I like.