Your dog is standing at the edge of the sea or a lake, and you are deciding whether to let them in. It is a fair thing to be unsure about.
Swimming suits a lot of adolescent dogs. It is low impact, it tires them without the fast repetitive running that revs them up, and it is genuinely enjoyable. The hazards are all in the choice of water.
Choose the water before you choose the day
Look for a gentle shelving entry your dog can walk into, rather than a drop off a bank or a wall.
Find the way out before your dog goes in, and make sure there is more than one. A dog who can get in and not out is the main way this goes wrong.
Say no to moving water. Rivers, tidal channels, weirs and anywhere with a visible current are not first-swim places.
Say no to water with a green, blue-green or paint-like scum on the surface or the shoreline, and to water with a warning sign up.
In the sea, check the tide and whether it is going out. An outgoing tide takes a swimming dog with it.
Safety note
Blue-green algae blooms in fresh water can be seriously harmful to dogs. A dog does not have to swim to be exposed, because licking wet fur or drinking at the edge is enough. Do not let your dog into or near water with a green or blue-green scum, discoloured water or an algae warning sign. Call your veterinarian immediately if your dog has been in water like that. Do the same if they are vomiting, drooling, unsteady, twitching, weak or collapsing after being near water. Say the dog may have been in contact with blue-green algae. This is not something to watch and wait on.
The first swim itself
Let your dog put their own feet in. Stand in the shallows yourself and let them follow, without lifting them or carrying them out.
Keep the first session to a few minutes. Swimming is harder work than it looks, and a tired dog in water is a problem.
Use a long line clipped to a well-fitted harness in the shallows if your recall is thin, and keep it short enough not to snag.
Throw nothing far. A retrieve into water sends a dog past the point they would have chosen to stop.
End it while your dog still wants more, and walk them dry rather than going straight into the car cold.
Cold water is its own thing. Water that feels bracing to your hand is cold enough to shorten the session. A shivering dog, a dog swimming low in the water, or a dog who turns for shore is telling you to get them out.
Never force a reluctant swimmer
Some dogs do not like water, and carrying a hesitant dog in or throwing them off a bank makes that permanent. Nothing about your dog's life requires swimming.
Working below the level that pushes your dog past their limit is what lets new learning stick. In water, that means paddling depth for as long as it takes, or not at all.
Afterwards
Rinse salt water and lake water off with fresh water, especially the belly, the armpits and between the toes.
Dry the ears gently with a cloth, and speak to your veterinarian if your dog shakes their head or scratches at an ear afterwards.
Offer fresh water so your dog is not drinking what they were swimming in.
Today's version, in one line: walk the shoreline first, find two ways out, then let your dog wade in for 3 minutes.