Poodles are normally good swimmers, but since yours could not get out of the water and you have no idea how long he's been in there, he might suffer from hypothermia. Lack of oxygen because of being in the cold water too long might damage his vital organs. It's best if you send him to a vet and have a thorough check. You can try Hands N Paws at C-17G, Jalan PJU 1/45, Aman Suria Damansara, Petaling Jaya, Selangor - 03-7804-6539. Quite reasonable or UPM. I don't know where's near for you but I hope you do send him for a checkup

Based on the symptoms you've been describing, it still sounds like effect of hypothermia to me personally (but as said I'm not an expert and since the vet thinks it's poisoning). As in humans, prolonged exposure to 26C water can also lead to hypothermia. (Click here and read about Canine Hypothermia) Try keeping your dog indoors and warm. Hope it's nothing severe. Do keep us posted

This is really sad news but the continuous seizure wasn't a good sign already =(. I hope the doctor didn't mention anything like canine distemper or parvovirus. But since your dog caught the virus from another dog in the area, I would suggest you bring your beagle for a check up for prevention.