It's called the Rosario Strait. It really does resemble a very gigantic river, and when the conditions are right (or wrong, depending on your perspective) it resembles a gigantic whitewater river. I've been out there crossing it in such conditions, and, while I wasn't exactly scared, I was uncomfortable. It was a gigantic wavetrain of exploding waves. I ferried across it with an upstream ferry angle that was extremely difficult to maintain (for, like, 2.5 miles). Not exactly like what you encounter on the river. Different. More chaotic (When an ebb tide meets a strong enough wind coming out of the south, about 15 knots or greater).

 

Then there's the huge standing wave I found once in Peavine Pass-- As big as any wave on the Wenatchee, I surfed it for minutes, then paddled over to shore and rode an eddy about 1/2 mile up to it again, ferried out to it, and surfed it some more.

 

And of course let's not forget the bigwater class III rapids that can be found at Colleville Point (Where the Strait of Juan De Fuca floods into the Rosario Strait, just off the southern tip of Lopez Island: I was there on a flood tide, and the current rips around a small group of islands  creating a very solid class III rapid with slots, holes, a pillow move, several eddies and a wave train. You can also attain back up to it and run it again (but this is every bit as difficult as attaining on the river and requires perseverence- it's a long distance.