Based on a 1927 design by Dr. George Kemmerer, University of Wisconsin, the Kemmerer bottle has long been favored by limnologists and fishery biologists. With few moving parts and a foolproof trip, it offers a trouble-free life. A key feature in the Kemmerer is the automatic lock which keeps stoppers open before the sampler is lowered. The seals close by dropping a messenger. When the sampler is closed, the entire weight of the sampler and contents is carried upon the lower valve. This forces the sampler to sit securely on the lower valve and prevents water leakage. A drain in the bottom stopper draws off water for analysis.