Why are there many swamps and lakes in the tundra?

Since the tundra spreads in the northern latitudes, where the sun’s rays hardly heat the ground throughout the year, water accumulates in the ground for centuries. This led to the fact that herbaceous plants disappeared in most of the tundra, and mosses and lichens began to grow in their place. Densely growing mosses and their roots (rhizomes) further retain moisture, and vast areas become swampy. And the lakes were formed in these latitudes after the last ice age, when a mass of ice pressed the ground where water was collected.