what aquatic animal, not bird, makes a rhythmic honking noise?

I live in central Florida and there is a canal that runs along side my house. Everyday I hear this honking sound I guess you could say. It always happens 5 times rhythmically and then it stops and sometimes I can hear a response down the canal. I have searched the internet to try and figure out what it could be but I have yet to find a match. I don't think it could be a frog or toad because it sounds far too deep, and I compared the sound to an alligator mating call and still no match. Someone please help because it's driving me crazy not knowing what it is...