Boaters, particularly jet-skiers, have fallen increasingly under fire in places like Lake Tahoe where a possibly carcinogenic gasoline additive, methyl tert-butyl ether, or MTBE, has been found permeating lakes used for drinking water. To provide background for policy decisions -- such as a recent move to ban jet skis at Tahoe by 1999 -- researchers from UC Davis are using a nearby Sierra lake as a liquid laboratory. They want to know from an ecological standpoint exactly where the MTBE comes from and what happens to it. Since March the UC Davis Tahoe Research Group has sampled Donner Lake from three sites, from the surface to the bottom. John Reuter, leader of the project, says that in nearly 500 water samples analyzed for MTBE, they have found concentrations of MTBE uniformly throughout the upper 40 or 50 feet of the lake. The levels increased to a high in mid-summer, most likely reflecting boating activity. The researchers calculate that about 815 pounds of MTBE were in the lake following the fourth of July weekend; the low was about 50 pounds, in the spring prior to boating season. While the levels are still way below drinking water standards, it's not yet clear how the chemical cycles through the ecosystem and whether there are any environmental impacts. The UC Davis team and their collaborators will continue their research at Donner Lake until next spring in order to cover a complete annual cycle. A summary of the Donner lake MTBE project is available at the Tahoe Research Group's web site, http://trg.ucdavis.edu.