Algae Blooms: Ponds and lakes are prone to blooms of algae in hot weather. Look for signs and notices to warn people against swimming. If in doubt, don't let your dog swim.
Poisoning: Slug pellets and other garden pest repellants abound at this time of year. These can be fatal to a dog if injested so check the lables of your pesticides and only choose pet safe products. Dogs are more likely to have access to garden sheds during the summer months too. Beware all those chemicals you store in there - who knows what your dog could get into.
Sores: Grass seeds are notorious for getting between paw pads, up noses, in ears and into throats. They can cause life threatening complications if left untreated. Give your dog a once over after every walk to pick up any problem quickly.
Summer parasites: These abound in the hot weather, so be sure to follow a strict worming and flea treatment regime. Don't forget to check the bedding too! Strict hygiene with food will help to prevent worms.
Hot Stuff: All dogs love to sunbathe but there can be too much of a good thing. Make sure your dog has access to cool fresh water at all times and plenty of shade. White dogs are particularly prone to sunburn so use a good canine sunblock before they go outside. Keep walks to the cooler parts of the day to avoid heat exhaustion and carry water with you at all times. The main symptoms for heat stroke include excessive panting and drooling, with the more severe cases losing conciousness. If you think your dog has heat stroke dampen a towel with cool water, wrap it round your dog and call your vet immediately.