This is something that is usually self taught in a bad situation, so here's a few tips that may help you out.
The channels and passes in our area produce some strong incoming and outgoing currents. You should always pay attention to what the tide is doing and where you choose to ride. Many times the current can be used to your advantage in light winds, but dropping your kite or board can put you in a bad situation real quick, so always kite with an experienced friend who can keep an eye on you. A good flotation or impact vest can save your life, as well as protect your body against impact. It also makes getting the board on your feet much easier in deep water!
With opposing wind and current, you will be more powered than usual since the current is helping to pull you upwind. If you crash your kite in the water in this situation, you will be faced with very tight lines and your legs out behind you in the current. Not usually a serious issue with bow kites (just pull a back line and hold it to relaunch), but If you fly C-kites, the tension in the lines will not allow you to roll the kite into the launch position.
SOLUTION- Use a 5th line on your kite to help with relaunch, or pull in 10-15 feet of your front lines and let them go. This should be enough to allow the kite to roll over. If this doesn’t work, use traditional self rescue, or upwind/offshore method before you are too far away from land.
When wind and current are in the same direction, you will feel underpowered due to the current taking you downwind. Crashing your kite can create slack in the lines and render your relaunch efforts useless. You will also be getting pulled rapidly downwind, so don’t hesitiate to self rescue using above listed methods. Beware of kiting around passes, as water flow extends well out, and to either side of the channel. This can create long-shore (sideshore) currents, as well as dangerous rip currents. This also occurs with wave action along the beaches. Undertows are created when waves crash on the beach and receding water creates a strong outflow of water under the crashing waves.
SOLUTION- If caught in a strong current, secure you kite and swim parallel to the current until you are clear, then use self rescue to pull you to shore.
Always pay close attention to warnings of rip currents, as they can cause stong undertows, which are extremely dangerous. Currents can also be much stronger in narrow passes, channels, and higher tides. Make sure you know the area you're kiting in, and NEVER KITE ALONE!