Did you know yellow bellied snakes are very scary because they are one of the most poisonous snakes in the world. It does not eat people it eats fish, eggs and small fish also it eats eels. It can breath underwater for up to three hours.
The body is normal but the tale looks like it got knocked down flat by a hammer. Usually you can not find snakes in New Zealand water because they like to swim in warmer water.
If you find a snake you will have to call the Ministry of Agriculture and Forestry and tell them what you have found.