
If required the whole equipment can be rented. You will get modern devises which are especially made for use in cold water.
Other requisites: diving certificate, valid physical examination, health insurance, your own equipment if possible.
Visibility varies in summer months. In June, shortly after the ice is gone, you might have a visibility up to 30 m. When solar radiation is increasing more and more algae are forming. In July and August the visibility may decrease to 6-8m.
However, when you decide to go diving in the lake Baikal, you should bring some dive experience in cold waters.