From the "I've never seen that before" department...

[Relic]

Not tortoises, but a pair of Three-Toed box turtles copulating in their pool. The female on the left actually has her head underwater (she raised it later after the photo shoot). I've had box turtles for over 50 years, seen a lot of weird things, but never this...

 

[TechnoCheese]

Woah!

 

[NorCal tortoise guy]

Cool picture!

 

[Beasty_Artemis]

Wow! How interesting. You learn something new everyday.

 

[Toddrickfl1]

I think it's possible they were on land first and then accidently fell into the water

 

[Relic]

My guess was she had innocently come to the water to drink, then male couldn't resist, forcing them both forward into the water. Had to admire his tenacity - he never let go...