I live near two ponds whose water levels appear to differ by a few feet. The ground is hard clay, so I don't think there's any underground water exchange between the ponds. The ponds are separated by about 30 feet of a bumpy terrain, with the bumps reaching a few feet above the "higher" water level. What is the cleverest way to determine the difference in water levels between these ponds? What comes to mind is to stick two poles (several feet high) at the water line in each pond, stretch a string between them, level the string with a bubble level and measure the distances between the string and the water level on each pole. Any other ideas?