Dave,
Mother Nature has sure given you her greatness where you live...and you clearly have a real knack for being in the right place at the right time...so much of what great photography is all about. 10-15 feet is truly remarkable! This is indeed a rare occurance and a real fortunate one for you. More so than a Beaver, Muskrat, or Mink, the River Otter are very curious and are more forgiving to intrusions...these look like young Otters and I suspect Mom may have been nearby.
Congrats to you and thanks for sharing.