Mercury in fish is a public health concern. People are sometimes advised against eating wild caught fish because of high levels of mercury. The data in mercury.txt were collected as part of a survey of lakes in Maine. The 120 lakes in the study were a random sample of all 1073 'fishable' lakes and ponds in Maine.
The response is the average mercury concentration in fish muscle, measured in parts-per-million (ppm). (Aside for the fisheries folks: care was taken to ensure that the fish species and size in the sample were comparable between lakes). Various characteristics were measured on every lake. These included physical characteristics like elevation, surface area, maximum depth, and drainage area, geographic characteristics like latitude and longitude, biological characteristics like whether or not the lake stratifies in summer, and its trophic status, and whether or not the lake was formed by a dam.
The investigators had two goals: 1) Develop a model to predict fish mercury concentration in unmeasured lakes. 2) Estimate the difference in mercury concentration between lakes formed by dams and lakes without a dam (a natural lake). There are valid hydrological reasons to suspect that a dam will increase the mercury concentration. The other measured characteristics may also be associated with the mercury concentration and / or the presence of a dam.