When axolotls are in small areas of water, such as the clay pools in Lush Caves that they naturally spawn in, they will keep their velocity on land that they had while in the water, not slowing down unless they have been out of water for several seconds. This exists regardless of if the water block they are trying to reach is on the same Y level, or a different Y level.

Theory: This may be caused by axolotls pathfinding short distances over land to water, from water.