Skeg

From Kayak Wiki

The skeg on a kayak is a movable fin that's placed near the stern of the kayak. The skeg adjusts the kayaks centre of lateral resistance, i.e. it stops the back sliding across the water. Most skegs are made from plastic; these are adjusted by slides usually located torwards the front of the cockpit. Although all skegs have sliders they work in different ways; some are wire - they work on a push / pull system. Others are string and elastic and some are now hydraulic; each has its own pros and cons. If serviced regularly and properly all work equally well. [by Richard Cree, Ocean Paddler Magazine - Issue 008]