I've dove in a few lakes around Alberta,
West Twin, Sylvan, Pine, Forgetmenot pond, Minnewanka, and the submarine tank in West Edmonton Mall.
I've rarely seen fish in Minni, and most of the other lakes I've dove in were too silty, except for WEM.
I don't think there are a lot of spearfishermen, so the pressue is pretty low. That being said it would be pretty tough to even get close enough to one IMO.