Sharking is an old but solid technique that shows up a lot in Valve games. Anyone can do it, and it can really give you a legup in some unprofitable situations.
Originating from the original GoldSrc engine and surviving even to today, ‘sharking’ involves keeping the jump button (probably space bar) held down while landing in or entering deep water. The character will ‘surf’ along the top of the water maintaining their momentum, instead of sinking and blimping along underwater. Great for avoiding the dreaded slowdown of swimming.
As an avid sticky-jumper I love sharking, its one of my favorite mechanics in TF2. Certain maps, like the newly added koth_moonshine, have lots of water and the player who can jetski across finds themselves at a significant competitive advantage. If you can aim for water, you can avoid fall damage at little cost. Balloon race is, for all its flaws, a great map to practice this. The sewers of 2fort or the canals of well are great maps for practicing normal sharking since they contain high-combat water areas where it becomes important to traverse them quickly to get out of harm’s way.
So, if you’re not already, start sharking and see what you’re missing out on.