I've know a few people who dig out old cans from drained lake bottoms. I've dug a few myself. Sometimes they will come out in real good shape sometimes not so good, depends. The colors usually do change especially the reds like to turn dark maroon. If they are found deep in the mud they get better protection, with no oxygen not much rusting. Some of mine below. LEON.
How cool! They're in great condition too. I occasionally find a clay beer at a dig site, but they're usually banged up or broken at the neck. That bottom silt and mud are far more gentle than old trash dump fill.