The cause of the rings is methane gas, released by decomposing organic material, which lies on the bottom of the canal. Dead plants make up some of it, but mostly, it's human feces, which end up in the canal during rain storms when the combined sewer system can't handle the increased water flow.
Since August last year, he has monitored the canal almost daily to shed light on the health of one of the nation's most polluted bodies of water.
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