16 October 2015 Last updated at 07:14 BST
Stig's specially trained to hunt out where water voles have been going to the toilet.
It might not sound like a nice job, but it helps wildlife experts keep an eye on where the water voles are living and how the population is doing.
Stig can reach areas along the river bank that would be very difficult for humans to get to.
Ricky went to Thorley Wash Nature Reserve in Hertfordshire to see Stig in action...
Meet Stig, the Springer Spaniel who's thought to be the world's first water vole search dog.