I don’t know if this is an east coast or Atlantic Ocean phenomenon, but has anyone else ever experienced a “warm spot” while swimming where the water feels about 10 degrees or so warmer then the surrounding water.
(I really don’t think that “peeing” is a valid explination…I’ve experienced these many times when I was the only person around and I have excellent bladder control) 
I’ve experienced these back when I used to swim off of Jersey’s coast. I just thought it was my immagination. 
My WAG is that the water in that spot has been heated by the sun, and has not been mixed with cooler deeper water for whatever reason yet. Maybe some sort of stable localized circulation pattern that keeps a blob of water from mixing with water around it.
Ever seen a whale pee? 
Seriously, thermoclines. Same thing submarines hide under. SCUBA divers will often hit them between 10-25 feet also. Only difference is the ones subs hide under are a lot deeper.
not really. i swim once in a while, off the north coast of singapore (look for the malay peninsula below thailand, singapore’s at the southern tip of the peninsula). the only warm spot i get is when i’m approaching the beach. about 10m off the shoreline at high tide the water starts feeling very cold. but it’s probably only about 5 deg C rise. I’m attributing it to ground warming - the sun here is too damn hot.
in your case, i don’t really know though. could be something hot under the sea…where were you exactly? near the shore or in the middle of the ocean? mid-atlantic rift?
This happens to me frequently at the Jersey shore. Not quite sure why.
In Jersey it is the “pee” for sure
We have a power plant down here that used to (it might still) discharge warm water from a subsurface outlet. And the Gulf Stream runs up the East Coast with temperatures that look like they might get up to ~70º, which would feel warm, I think. Aerial photos I’ve seen show a very clear line of water color change demarcating the edge of the Gulf Stream current, one that might not be noticeable while swimming.
I’m at the Jersey Shore. 
It’s generally a small area, maybe 1 ft. in diameter. I only swim up to a depth of about 7 or 8 ft. but I notice it from maybe 5ft out.
This is a great question.
While I have never experienced this warm spot thing. I have experience with the inverse, the cold spot.
While swimming in the warm oceans of the South Pacific. Many places when I was snorkelling or inner tubing well out from the beach and suddenly hit a cool spot surrounded my soupy warm water. They are lots of fun to find when you’re baking in the hot sun on an inner tube, suddenly a lovely and cool spot.
So much for the pee theory!
I’ve experienced the same thing inlakes and creeks (or bayous down here). I have experienced both cold and warm spots. I always assumed it was due to springs.
While cringing in the frigid English coastal waters, I have only ever dreamed of happening upon a warm spot. Colder spots are the norm here. Hell, as kids, our Mum would bestow a boiled sweet upon the child who could remain submerged up to the neck for the count of 10. She counted slow, and we amazed each other with the lovely shades of blue we could turn.
Whenever im in the water at Corona del Mar, I get one of these “warm spots” every 10 minutes or so. I got used to it but id like to know what it is also.
sand lake near where i live has da’ spots, some warm, some cold. i go swimming alot. maybe i will make note of where such spots are the next time i swim. the time after that i will see if they are still in the same spots. i believe the lake is warm spring fed. i have not seen anything anything to conferm this, but the fact it warms up about a month before the other lakes seem to conferm this
I live in NJ, so ignore the fact that I don’t know whether this happens anywhere else. But it does happen here.
My question: Like ChryslerBldg, I think most of these warm spots are rather small. My question is: Regardless of how they get heated, what prevents the water from mixing with the other water and immediately averaging out? I would think that in a rapidly mixing volume of water such as a beach, you’d never find such sudden and drastic temperature differences.
Thaumaturge got it in one.
Ordinarily, if the water were still, the upper parts would be sun-warmed, and the lower parts would be colder. And, in fact, at the beach, when you dive (say in six-foot depths) you can easily feel the difference. The bottom is quite a bit colder.
But then you have those nice combers and breakers, coming in, churning stuff up, stirring big globs of water around.
And so, now and then, a big blob of warm water will mooble along (technically speaking…not!) at three-foot depth. It does, indeed, feel just as if you’d encountered a bolus of whale-whiz. But it’s just a randomly moving hunk of surface water.
The same effect works in reverse, and, in the wake of a good breaker, you’ll sometimes hit a pocket of cold water that has been brought up from the bottom.
There is a technical term for these pockets of water that maintain a limited degree of cohesion, but doggone if I can remember it.
(It’s also vaguely involved in the reason for the “net-like” appearance of light at the bottom of a swimming pool. The water globs together in blobs – technical language again! – and they act like lenses.)
I used to know a guy who knew this stuff cold: he was involved in early computer animation. He was one of the pioneers of making “Jello” semi-solids bounce around the way real Jello does.
Trinopus
The “net-like appearance of light at the bottom of a swiming pool” is called caustics.
Ale, another computer animator.
Going back to the topic, Trinopus, your explanation seem right, but doesn´t explain why I have experienced very warm spots of water on calm sea conditions. Something keeps telling me that this is associated with salinity changes; I live by the River Plate, when a very large mass of fresh water meets the Atlantic, somedays there`s a salty sea and somedays there´s a fresh river… it´s really amazing. Anyway, I know that fishers here take water samples to look for fresh water or salt water pockets, in search of a certain type of fish; whatever keeps those pockets it´s a mistery to me.
I think that the same phenomenon can be seen too, when the sea/river is calm there are some areas that have a distinctive surface difference compared with the surrounding water, seems that the water is more still in those areas. Usually they have the shape of a stream, or a water river, so to speak.
I was in Kefalonia a week ago and was hardly ever out the water. We encountered these warm spots often. You know when your in a clear sea and there are little green patches and white patches in the water? Well when I swam out to the white bits I found that it was just white rocks on the sea bed and these bits were definitely colder than all the other bits. When you float on your back the water always feels warmer because you are at the surface. I think the swimmer may help create these warm spots by moving the water around.
One of the reasons may be biological. I know that if you hold your hand over a sponge the water coming out of the top of the sponge is distinctly colder than the sorrounding water. I magine that coral, and other organisms like that affect the water temperature, and as others have explained, warm and cold water don’t mix right away, thus creating warm, or cold spots.
Shameless bump, I´d like to know the answer to this one.
I once hit a thermocline whilst diving at around 60 feet off the coast of southern Spain. Within inches the water had turned from a comfrotable temperate to being frigidly cold. You could be swimming in warm water above the thermocline and put your hand down below you and you’d need to raise it again within a few minutes.
Perhaps these are just small surface thermoclines? I’ve experienced the same effect on the surface as well.