The signature bird of the northern forests, the Common Loon, is an adept swimmer and diver, a speedy flyer (up to 70 mph on migration), but a pathetic walker.
Pushing the adaptation for efficiency in the water by moving the legs far back on its body to act like propellers has made this bird totally unsuited for a terrestrial existence.
Walking on land requires leg placement under the body, not behind it, such that the center of gravity of the mass of the bird is more or less right over the legs which support it.
Loons only come on land to mate and to tend to the eggs in their nest, which they place close to the water’s edge. Instead of getting their legs under them to stand upright, they use those rear-placed legs to shove them forward on their bellies.
And as the video below shows, their movement onto their nest is slow and awkward. (You might want to turn down the volume of sound when playing the video. The loon moves onshore to its nest at about 0:40 into the video.)