The Grass Snake (Natrix natrix) is a Eurasian non-venomous snake.
It is dark green, brown or grey in colour with a characteristic yellow collar behind the head, which explains the alternative name Ringed Snake.
The underside is whitish with irregular blocks of black.
Grass Snakes are strong swimmers and are often found near fresh water.
They feeds almost exclusively on amphibians.
Not being venomous, the snake's main defence is to produce a garlic-smelling fluid from the anal glands, or to feign death (thanatosis) by becoming completely limp.
They may also perform an aggressive display in defence, hissing and striking without opening the mouth.
They rarely bite in defence.
When caught they often regurgitate the contents of their stomachs.

1st photo: A juvenile (25 cm). Landgoed Oostbroek, De Bilt, The Netherlands, 4 September 2018
2nd & 3rd photo: An adult (80 cm). 's Graveland, The Netherlands, 11 August 2012
4th & 5th photo: An adult (110 cm). Bachlaan, Hilversum, The Netherlands, 26 May 2018