I thought I'd better put this info about dogs overheating in still waters as the waters heat up with the weather, plenty more info if you Google but heres a useful start:

http://www.petplace.com/dogs/be-a-cool-owner-don-t-let-your-dog-overheat/page1.aspx
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I've not read this article yet, but it is timely to warn people about their dogs when the temperatures rise.   And the sea is warm right now too - abnormally so.    I'm always mindful of how HOT beaches get and although it might seem a good idea for a dog to go to the beach, this isn't necessarily so.   Early morning/late evening and on dog-friendly beaches may be fine but otherwise most dogs are far better left at home in the cool during the hottest part of the day when we human idiots, insist in being out there!!

As for ponds - be warned about algie.

General rule should always be to exercise, and feed, during the cool part of the day and provide shade (cold tiles on the floor), fans and air.con with loads of fresh cool water, when it gets hot outside.   Dogs generally are far more sensible than we are and have the ability to zonk out when we can't.   I always cut back the amount of food during hot weather - if only because less exercise = less need for food.

It's really just common sense.   And I've seen two cases of heat stroke in dogs ( not my own) - one survived, the other sadly didn't.