You may not have noticed but you are also describing an inborn fear of deep water.

Does the dog fear drinking water? No. So the dog specifically fears deep water. What taught him to specifically fear deep water over a bowl of water? Most likely he was also born with the fear.

This also tells us that evolution often results in conflicting instincts… a fear of water and an instinct to swim. Most likely what occurred here is an early ancestor of the lab originally feared water and was not adapted to swim well. The feature that allowed it to swim well came later and is sort of like retrofitting a car to swim. You need to wait a really long time for the car to evolve into a submarine (see seals). Likely much earlier before becoming a seal an animal facing selection pressure to go back into being a marine animal will evolve away the fear of deep water. It’s just that labs haven’t fully hit this transitional period yet.

Is it fear of deep water, or fear of walking on a strange surface that might be unsafe? How does a dog know water is deep? Does a dog think its water bowl is deep?

You can pen a horse by painting stripes on the ground around it.