There are so many factors involved in both actual speed (short term) and perception of the “thickness” of water you’re paddling through that I think its hard to be very objective.
Ever try to paddle downstream fast on a river, like if you’re trying to catch up to someone or get to a landing a few miles away when the weather looks a bit iffy, and cross a strong eddy line without turning in? Like when you’re pulling hard on a paddle with the current at your back and suddenly you’re pulling hard against an temporary upstream current? If you’re not expecting it there’s suddenly much less resistance on the paddle… Like the water suddenly turned “thinner”. Its pretty easy to wobble a canoe doing that if you’re inexperienced and not expecting it. Feels like pushing on a bicycle peddle and it just drops down a gear without your input. But its a just a perception - I’d bet dollars to doughnuts that equal volumes of water taken from either side of that eddy line weigh the same. There’s no difference in density. The water isn’t thinner, but it feels that way.
Shallows can do that too… ever notice that if you’re just cruising along nicely, paddle, glide, paddle, glide and you hit shallows? Lake or river, current or not, suddenly the glide just gets cut in half. If you’ve got a full load of camping stuff your momentum can carry the freight train on for a bit, but soon there’s a noticeable difference.
I’m not a racer but I’ve known and paddled with a few. They make serious study of such things. Pay heed to what they say, they usually know that of which they speak. I’ve observed that the words “suck water” sometimes leap unbidden to their lips on such occasions.
A level of plane thought, perhaps development, that was planted in my brain long ago by someone who used to post here was that a wake was a three dimensional thing - a moving (non-planing) displacement craft (canoe of kayak among others) displaces water downward as well as parting it to the sides where we can see it. The faster the boat is moving the greater the wake (though as I understand it the angle of the wake is constant - no matter the speed or the shape of the boat… odd, eh?) When that downward vector of the wake hits a shallow bottom and reflects back against the hull the density is actually a bit greater under the boat. “Thicker” water is the perception. (Feels more like a coasting on a bicycle on pavement and hitting a patch of mud - the coast gets bogged down a bit.) But perhaps that’s all just an idea planted in my head, a level of thought that may or may not be indicative of actual reality. A meme I’ve just propagated… Perhaps there’s a better explanation for the slowing that is real enough.
Whatever the reason, I still prefer to paddle in a little deeper water where I can get in a decent paddle stroke.
On a few occasions on lakes I’ve noticed, and not consistently, that not all my paddle strokes feel as though they’re meeting equal resistance. Its a bit like the eddy crossing situation but more regular and far more subtle. It feels like the water is thicker, then thinner, then thicker, etc. It was a perception I took to be a misperception until I learned about Langmuir currents.
It seems that wind on a lake can produce shallow (depth of epiliminion) circular currents. Visualize a series of pairs of big horizontal rolls of carpet rolling in opposite directions. Lines of foam form where the currents sink. We’ve all seen those, right? When paddling across them at a right angle they can sometimes be felt on a paddle.
Of course when paddling some distance from a shore where there are fewer ready points of reference it can feel like you’re paddling and paddling and paddling but not getting there. But that really is a misperception. (reason tatters in ice petal flowers revolving)
