Water supply pipe
 

Wondering if anyone has any tips on locating our water supply pipe at the bottom of the lake? Bought a lake house last year (small lake in Maine, not Winni) and tried all summer to find our waterline. Thinking it is buried and pops up away from the shore but unable to locate it. Lots of dirt on our filter after the pump. Any tips?
Thanks in advance for the advice.

Easy
 

Make up a fitting at the pump inlet and put some compressed air back thru the water inlet. The bubbles will lead you right to the waterline.

Foot valve
 

Will you get the bubbles if you have a foot valve? Or is one not necessary if the pipe is in the lake

No, that is the purpose of a FV, to prevent back flow.

Maybe put on a diving mask and some flippers, and go diving round in a likely spot in maybe six feet of water.

Maybe you could push a wire down the line from the house, then use it to locate the path of the line from house to shore, much as is done when a gas line with tracer wire above it is located. If you know the point on the shore where the line goes to, that ought to narrow down the part of the lake to search for the inlet.