Most of the terrain consists of a large body of icy water, cold enough to even pierce through any sort of cold resistance that Link is wearing on him at the time. Furthermore, Link should avoid swimming in the water at all costs as he will take damage very quickly from the very cold water. Link should also not come to this place unless he is wearing cold-resistant clothing, such as a Warm Doublet, the "Snowquill" set of armor, or have cold-resistance food and elixirs on hand before entering the area.
On the eastern mainland, there is what appears to be a destroyed cottage of wood with a non-functioning Guardian. To the right of the destroyed cottage, there is a Cooking pot for making any cold-resistant foods or elixirs. On top of the boxes, Link can find a Korok Leaf and Link should use it for steering the raft and sailing between the two mainlands though this is one method of getting across. Alternatively there is a broken archway further downriver with more non-funcitional Guardians which contains a metal door which Link can lift with Magnesis Rune to create a makeshift bridge across the water by carefully placing it on top of some old bridge supports that once held up the eastern side of a wooden bridge, allowing Link to reach the surviving remains of the wooden bridge's west end on the other side. Both methods would be nullified assuming Link has Revali's Gale, since he'd be able to fly across the body of icy water, if he has any charges left. It is also nullified even much earlier once Link acquires the Cryonis Rune as it allows him to create Cryonis blocks on the water to use as stepping stones though he must be careful to avoid falling in.
On the western mainland stands the Keh Namut Shrine, which houses the Cryonis Rune and a small body of water next to the Shrine, which is also consistent of icy water. A Korok hides under some ice on the wall northwest of the Shrine. On the southern mainland, there is the range of Mount Hylia and on the northern side leads to Hopper Pond and the Forest of Spirits.
However Link can use its freezing cold water to free raw meats, poultry, fish, snails, and crabs to create frozen food dishes. However he should drop them from the raft or near the shoreline to avoid having to enter the water to retrieve the frozen food.
River of the Dead is likely a reference to its cold waters being lethal and the fact it is essentially a cold lifeless river devoid of life as not even fish can swim in it. Its name may also tie in with the nearby Forest of Spirits as both reference death and spirits.