The factors determining whether today's a good day to paddle are usually weather -- is it too windy? No visibility can mean no paddling because of too much fog or snow (both have cancelled paddling for our group, once back in 2006) or that smoky orange haze last week from all the forest fires. Of course some gung-ho kayakers figure that any day the sun comes up is a good day to paddle and they're willing to overlook when it might be nighttime. But for urban paddlers, the E. coli count is another factor.
At beaches where a lot of people want to enjoy the water and shore, local health authorities test the water for germs of various kinds. One of the most important is Esherichia coli. Good ol' E. coli is not something you want a lot of in water where you're swimming or even paddling. As my friend Todd Wong says, To paddle or not to paddle at the beaches of Vancouver -- that is the question. An E. coli count of 10 per 100ml for Kitsilano Beach? Fine! But 1184 in East Bay of False Creek... ooo, ya don't want to go there.
Check out the Beach Water Quality Report for the Vancouver area this month. There are some beach postings here by the Vancouver Island Health Authority. Here's a link for Ontario beaches; if you live somewhere else I'm sure you can find your local water quality report or beach warnings.