Answer:
The maps show that Lake Baikal has very little agricultural production around it, a very sparse population density, and almost non-existant industrial zones.
In other words, Lake Baikal is located in a sparsely populated area of Siberia, with only a few towns, and a few agricultural belts around those towns. This in part can be explained by the fact that Lake Baikal is sorrounded by mountains in many areas, which is also why the lake is so deep.
The lack of intense human activity is what contributes to the relatively pristine character of the lake today.