Small dog, big water
Most Chihuahuas do not like swimming, and the reasons are practical rather than temperamental. A Chihuahua may weigh less than a bag of sugar, stands only a few inches tall, and experiences a garden pond roughly the way you would experience a lake. Water that is a paddle for a Labrador is over a Chihuahua's head. Add a fine or short coat, very little body fat and a high surface-to-size ratio, and deep water becomes cold, exhausting and frightening for this breed very quickly.
That said, Chihuahuas are individuals. A confident, well-socialised Chihuahua introduced patiently to warm shallow water sometimes discovers that paddling to his owner is a fine game, and a minority become enthusiastic little swimmers in short bursts. The difference lies almost entirely in how the first experiences are handled — choice and warmth, or pressure and cold.
Rules for a dog this size
Every Chihuahua swim happens on Chihuahua terms. The water should be warm — a sun-warmed paddling pool or a heated dog swim pool, not a bracing lake — and shallow enough for him to stand, so swimming is a few voluntary strokes between standing spots rather than a survival exercise. Fit a life vest actually made for a dog this small; a standard small vest can slip over a Chihuahua's head or tip him sideways, which is worse than none. Stay within arm's reach for the entire session, keep it to a few minutes, and lift him out at the first shiver, scramble or tucked tail rather than after it.
Garden pools are a serious hazard at this scale. A Chihuahua who falls in cannot reach the edge to climb out and tires in moments, so pools need fencing or a rigid cover and a Chihuahua should never be in a pool garden unsupervised. The same caution applies to baths, deep buckets and ponds on walks.
Warmth and drying come first afterwards
A wet Chihuahua loses heat fast, even on a warm day, and shivering that continues after he is out is a sign the session went too long or the water was too cold. Towel him dry immediately, wrap him somewhere warm, and let him rest — swimming, at his size, is a full workout. Dry inside the ears gently as well, since water in such small canals irritates easily. If a Chihuahua who has been in water seems lethargic, keeps shivering once warm and dry, or is coughing, contact a vet promptly rather than waiting, because little dogs deteriorate faster than big ones.
Hot weather changes none of the rules but does explain the appeal of trying: a shallow tray of water for standing and splashing in is, for most Chihuahuas, the perfect summer compromise — cooling without swimming at all.
Let the dog cast the deciding vote
Run two or three gentle, warm, shallow introductions and watch honestly. A Chihuahua who paddles back in by choice has given you a swimmer to enjoy short sessions with. A Chihuahua who climbs out and shakes himself at a distance has also answered, and overriding that answer for a photo or a laugh teaches him that water predicts being frightened. Many Chihuahuas live entirely happy lives as professional shore supervisors. Whichever yours is, writing it down prevents a repeat experiment by someone else, and KinsLe Family Sharing keeps your Chihuahua's water preference on his profile where family and sitters can check it.