When I am fishing on the beach during a cold day, and I don't feel like wearing waders, I wear the following:
A pair of very light water-proof pants, cut off mid-calf. I wear these over a similar length pair of pants.
I find that I can walk out to a depth over my knees in the water, and that waves and splashes of water don't shoot up and freeze my s off.
Hope someone finds this useful.
H.L.S
P.S. I also do this when rock fishing. This gear is also fairly safe if one is washed off, as does not restrict swimming too much. (although I haven't tried it personally )