Rassla Lake is a location found in Breath of the Wild.
Breath of the Wild
Rassla Lake is a body of water located just south of Lake Floria. Water from the Rassla Lake flows down a waterfall to the north, falling into Lake Floria. The Lake is surrounding on all sides by the Ubota Point.
There are four treasure chests found underwater within the Lake. Three are found right at the center of the Lake and they contain a Knight's Shield, Topaz gem, and five Ice Arrows. A fourth chest is found just east of the Lake containing some Flint.
Near the waterfall, there are a few Hyrule Bass that can be found swimming around.
Nearby Korok Seeds
Lift the rock.
Reach the block behind the puzzle using Cryonis (you can do horizontal pillars on the waterfall if needed), then solve the block puzzle.
Offer Mighty Bananas. Some are quite close by.