River Snorkeling?

On a walk through Rooks Park on the eastern outskirts of Walla Walla this weekend, my husband and I saw these two gentlemen playing in the water. The one in the black shirt was fishing (we actually saw him catch something later), but what the other was doing we couldn't be sure. He would stand about knee-deep and stick his face into the water, wearing a snorkeling mask. We never did figure out what he was doing. This is Mill Creek - one of the main waterways through the towns in the WWV. Many years ago, the city built Bennington Lake, a reservoir a mile or two upstream from Mill Creek (if you could walk straight from where this photo was taken, you'd run into it) to help control the flooding that had happened on multiple occasions. They also widened Mill Creek, and as a result, the river looks like it has steps, such as the one you see here. They are evenly spaced, creating a not-so-natural look, but it's fun to listen to, as there are multiple small waterfalls. As you can see, the water isn't very deep, either. Some places toward the middle get deeper, but it would be difficult (though not impossible) to swim underwater here. (Credit to my husband for this photo.)