Is a Jack Russel Terrier really smart?

I was working on a boat in a local marina with my dog, Rascal... He is a Jack Russel Terrier and has proved to be very smart... I started taking him work with me and occasionally let him run around the marina area... Well, one day he noticed ducks!!! He took off after them, they flew and he went into the lake... He swam around and looked at me with a suprised face... I reached down and picked him up... He definatly did not expect to land in water... He ran around for about 30 minutes and chased after several more ducks... It was a Kodak video moment...