Sharking, aka Water Strafing or Speedboating, is the act of gliding across the surface of a body of water. Sharking can be performed by simply jumping onto the surface of a body of water with jump held. The majority of the player's horizontal velocity will be retained as long as the jump button is held. Sharking players can turn in a manner similar to Bunnyhopping while retaining speed. I.e. turning is achieved by letting go of the forward key, then using the strafe keys & the mouse to change direction. If the crouch button is held, it slows you down similarly to holding duck while strafe jumping.
There is no speed restriction on sharking, as it is of limited use, but helps make movement feel more fluid and contiguous across several different types of terrain and obstacles.