Not diamondback rattlers, of course Connecticut is far too northern for that, but diamondback terrapins. 
I had never looked for this species before, so I wasn't exactly sure how I might see them or if they definitely occurred at this location. 

At this point I had not seen any turtles but a number of interesting birds, including the first Oystercatcher I had seen in the state. The search continued on until I noticed a small head bobbing in the water. Could it be the turtle?

​