What Fresh Water Snakes Are Poisonous?

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7 Answers

Rev. Dr. Charles Rogers Profile
Contrary to popular belief, the Water Moccasin commonly known as 
the "Cottonmouth" is the only poisonous water-loving snake in the 
United States. It is a large, very thick-bodied snake with a chunky 
head and a short tail that tapers very abruptly from the body. The 
inside of its mouth is noticeably white and the moccasin, when 
surprised, has a habit of rearing its head back, opening the mouth 
wide, and beating its short tail back and forth in a vigorous steady 
rhythm. It looks as mean and dangerous as it really is.

It 
inhabits swampy areas, bayous and rivers along the Atlantic Coast and 
the Gulf of Mexico from southern Virginia to Texas; and up the 
Mississippi valley as far as southern Illinois. It will eat birds, small 
mammals and the harmless water snakes but feeds principally on fish 
and frogs, so the cottonmouth usually does not go far from water. It is 
generally found on muddy banks of ponds, swamps or sluggish 
streams, on partly submerged logs, or on low limbs of bushes and trees 
overhanging such water areas.

Like most snakes, a cottonmouth will not attack if it can escape. 
Walking along a bayou southeastern Missouri one time, a huge one 
glided across the path, only three feet ahead of us, into the water. 
Quietly paddling a dugout canoe through those bayous, moccasins 
frequently dropped off of branches just in front of us, and swam away 
beneath the surface to shelter, in a growth of cattails.

The cottonmouth, like the rattlesnakes and its close relative, the 
copper head, is a pit viper. There is a deep pit, apparently a sense 
organ, between each eye and the corresponding nostril. There are, of 
course, two long hollow fangs at the front of the upper jaw, like 
hypodermic needles, for stabbing its prey and injecting the venom.
 
The moccasin' s scales are keeled and rough. Its color may be dull olive, sooty brown or almost black, with indistinct dark bands which 
disappear in older snakes that become 4 or 5 feet long. The young, 
from 7 to 12 in number, are born alive, bright brown and brilliantly 
marked, with sulfur-yellow tails.

See the attached picture...
thanked the writer.
Anonymous
Anonymous commented
Wrong on one point. A copperhead is venomous, though not deadly poison. A friend of mine was bitten by one, and his leg swelled to about 3 times normal size and was black and blue and VERY painful. They can make a person extremely sick, and theoretically could kill a person if bitten in the neck or some such.. but not one death has been recorded in Missouri from one, and we have lots of copperheads and water-moccasins.

http://www.ces.ncsu.edu/gaston/Pests/reptiles/copperhead.htm

Otherwise good answer.
Jeannine almeida
Jeannine almeida commented
The question actually asked what type of water snake...last I checked copperheads were not exactly famous for living in the water...also if you are going on other types of poisonous snakes don't forget the rattler. Water Moccasin would be the right answer. Nice try Billzbub.
Anonymous Profile
Anonymous answered
Copperheads love water as well.  I have seen many of them in fresh water creeks swimming.  They are also very aggressive, and they are known to camouflage their skin to their environment.  I would do a search on google for Freshwater Poisonous Snakes in California.  Anything is possible, but always better to be safe then sorry. 
Anonymous Profile
Anonymous answered
Does Copperhead in West Virginia swim in the water?
Anonymous Profile
Anonymous answered
Name 1 fresh water snake
Anonymous Profile
Anonymous answered
All snakes are poisonous. The government is trying to fool us into believing that they are not. Do not be fooled. Run as fast and as far from any snake you see. To be safer, always wear thigh-high snake proof boots wen running to your car from your home, and hang a few slices of cucumbers around your neck to ward off copperheads.

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