What is this geographical feature? (as seen in maps) Can someone help me identify this peculiar geographical feature I've noticed in satellite imagery?

This particular screenshot is from satellite imagery of northern Russia, however this kind of geography appears extremely common in the northernmost latitudes of both Russia, Canada, and the United States.
The below image is from Alaska.
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I've always wondered how this landscape would be described. Is this marshland, or swamps, or something else in particular?
Thank you!
The dark color of the water masses make me think they are peatlands in tundra.

Peatland is a terrestrial wetland ecosystem in which the production of
organic matter exceeds its decomposition and a net accumulation of
peat results.
The largest known concentrations of peatland are found in Canada and
Alaska, Northern Europe and Western Siberia, Southeast Asia, and parts
of the Amazon basin, where more than 10% of the land area is covered
with peatlands.

Source: peatlands.org