I Think Kermit is in My Pond

What Is This? RK called and said he saw a monster in our lilly pond (ok - a 100 gallon plastic tub). It's a 3" something with a tail and 2 legs. It's big and it's ugly!

RK sent over a picture of this monster. He couldn't believe it's a tadpole. It's too big and where did it come from?

I think it's a chubby tadpole becoming a frog. But RK is right, where did it come from? Our tub is tucked away at a corner against the fence. There is not even a tree around. Yes, the swimming pool is near by but it won't bring on frogs let along tadpoles. A tree frog? A toad?? A monster??? By the way, why only one? Aren't tadpoles groupies?

In Our Lilly Pond: We have 20+ some odd happy goldfish, and 4 -6 crawfish that escaped from becoming food (I hope they're still there), but that's about it. Hmmm... just don't eat my fish, ok?

Can someone explain how it might have ended up here?

... and can I kiss the frog?