Swimming is an innate ability with snakes, their anatomy allows them to hunt both on land and in water, and there are species which surely prefer water as their main life environment. Fresh water snakes are usually waiting for their prey under tree branches fallen in water or underneath overhanging trees. Hence, when on a fishing expedition, you need to take the same precaution measures as when you go hiking, climbing or camping and do your best to stay away from snakes. Some species cling to tree branches and once movement is spotted, they instantly drop; this is pretty risky if you get one of these poisonous species into your boat. Dealing with a frightened snake in the crammed space of the boat can be scary for anybody.
Some water snakes are harmless to humans while others are a real threat. If we consider for instance water snakes living in open seas, then, keep in mind the fact that they have been rated among the most venomous creatures on earth. Sea water snakes are so lethal as the concentration of the toxins has been adapted to their life environment: they have to strike fast and kill as fast or they lose the prey that flees or drops on the bottom of the ocean. Nevertheless, chances of getting bitten by salt water snakes are lower than encountering a water moccasin. Most of the advice given in survival guides consequently discusses the ways to deal with fresh water snakes that hunt in rivers, lakes or wetlands.
When you go boating one great tip is to always have some form of handled reptile grip tool if you have to cross river areas with overhanging branches. Practice with small and large hose pieces before you launch the canoe, so as to be ready for the least friendly of water snakes. If you spot water snakes swimming, these are not a threat to you, if you are on boat as they cannot jump out of the water. In case you get bitten, an identification of the snake would be of much help in case you need to administrate an antivenin.
You can recognize the bite of non-poisonous water snake by the horseshoe-shape. In case you get only two punctured wounds, then you most probably have been bitten by a venomous snake and you need to get to an emergency room immediately. A venom removal pump should always be present in the first aid kit in the boat as a means of delaying the spreading of the toxin in the blood and thus earning some more time before getting to a medical facility.