I KNOW it's there.

As kids we were told, in school, that frogs "...spent the winter under mud at the bottom of ponds....."

Forever learning - should have been the Blipname ...
"Frogs and toads normally overwinter in places like compost heaps, (NOT pond bottoms)  amongst dead wood or under decking/your shed/other objects. Some amphibians, usually frogs and sometimes newts, will choose to overwinter at the bottom of the pond; they bury themselves down in the silt at the bottom and take in oxygen through their skin.
Amphibians may choose to come out and forage during milder periods of weather so don’t worry if you see them around quite late in the year or if you accidentally disturb them."
I have never needed to investigate this, but was a wee bit gobsmacked when removing the old tomato plants to disturb a big fatty who hopped away and under a different Plant ring.
Since then I have seen a couple in the greenhouse.
I was even more gobsmacked to see life in the pond bottom. I'm in the Hobbit habit of wandering around the garden by torch light, especially since I changed the bulb for an LED.
1st thing I saw was a water beetle. Then a Frog which promptly did a Harry Potter and Disapparated 'neath the mud.
At time of writing I can guarantee no less than three which swan about after "Lights out", practically nightly. The pond being more stable in temp than the air.
One day I'll get a good shot.
BTW you can just make out the back right leg, almost dead centre of the thumbnail.