I have one that is digital attached to a probe that can be dropped into deeper water. I purchased one that is a DO/temp meter that no longer works on the DO side but the temp still works. Made in china crap. Or take a gal wide mouth jar, turn it upside down, dive to the deeper water turn the jar up and gather water and if you can hold your breath long enough then screw on the lid and swim the the surface, measure temp. Not a perfect way but it will work, I've done it.
