Earlier in the week, I snapped a photo of a strange incident in the park below my building. After some investigation, my sleuthing friend Matthew (of The Night the Aztecs Stormed Glasgow fame) solved the mystery:
It’s not a reservoir under there, the creek itself is the reservoir. The water spouts are a test of the False Creek Pump Station, part of the Dedicated Fire Protection System in Vancouver. Basically, in case an earthquake disrupts the normal water supply, there are salt water pumping stations to assist fire-fighting.
He kindly sent along this page from the municipal website and this page which has some fancier photos. Apparently they run this sort of test the first Friday of the month at 12 noon from March to November. I don’t know where I’ve been for the past 18 first Fridays, but thanks to Matthew for the closure.
DarrenBarefoot.com 
Imagine how flumoxed you’d feel living in the Midwest where at noon of every first Friday of the month big cities test the Civil Defense sirens. One stands about every square mile or so, peeking over quiet playgrounds or standing guard over bustling parking lots, and living near one can provide an unwanted adrenalin rush once a month. Eventually, when you know to anticipate the noise, the tests become reassuring. You see about a year ago a tornado passed through the area and we find out that the siren in our neighborhood wasn’t working. Now I listen for the test every first Friday at noon, my hand on the phone to berate city planners if the sirens don’t go off as scheduled.