Pond Section in Tank for Garter Snake?

Hi!

I recently got an albino garter snake named Squirt from a friend and he was telling me he was planning on building a little pond area with fish but never got around to it. I thought it was a cool idea and I want to execute his vision but after researching a little, I haven't found that anyone has done anything similar for their garter snakes.

My plan was to have 1/3 of a 40 gal tank set up as pond filled with guppies, with plexiglass or something separating it from the dry substrate. This way he can still have his warm and cool areas of dry land in the tank, but he'd also be able to have fun fishing too.

I still want to create this environment for Squirt, but I was wondering if it was safe.

If you have experience or knowledge on this kind of thing please let me know, thanks!!
-Nova

I also have a filter for the water area