On occasion it will be necessary to cross water, whether that be a river, a flooded road or some other aquatic obstacle. The most important thing to do first is to stop! Sounds obvious, but it is easy to make the mistake of thinking that because the track leads you to the river that it is automatically alright to cross. It most definitely isn't. The height of the water can vary from season to season. The strength of the current and the condition of the riverbed can also change depending on whether the river is in flood or not. Hidden obstacles like boulders, logs or deep pools may exist, which cause little difficulty to four wheeled vehicles but can drown of knock over a motorcyclist. These unknown factors are the reason that it is so vital to stop and at least look at the crossing you are about to undertake. Try to look for the shallowest crossing point, usually where the water is running fastest, near rapids. If you are in any doubt whether you can make the crossing safely, then cross on foot first. Getting a little wet is a better option than drowning your bike and/or you as well. Make a mental note of the depth, the condition of the bed and strength of the current. Make sure you know where your exit point is before entering the water. If the water level is not higher than your air intake and you can safely walk across the river then you can be fairly sure that it is alright to cross it on your bike. 

Before crossing it is worth taking a couple of precautions. Firstly spray all your electrical connections with an oil like WD40, unless you have greased or sealed these connections already. Secondly check that your carburettor and fuel pump's (if your bike has one) breather pipes are above the level of the water, as some bikes will cut out if these pipes are blocked. Ride slowly when crossing although try to keep your momentum going and, if you have walked it first, try to follow the route that you walked as closely as you can. 

Should you decide that the crossing is too difficult to ride at all, then you can push your bike across instead. Always stand on the upstream side of your bike to avoid the current forcing the bike over on top of you and trapping you underneath it. It is also probably a good idea to lighten your bike as much as possible by removing unnecessary weight like baggage. 

Should you decide that the crossing is too deep to ride or push without the chance of water getting into your engine then, once you are sure that there is no other option, you will need to prepare your bike for a submerged crossing. This type of crossing should not be attempted solo, at least get one other person to help or preferably two if you can. Start by spraying all your electrical connectors with a water dispersing oil like WD40 and removing all unnecessary weight like baggage. Turn your engine over to TDC (top dead centre) on the compression stroke (closes the valves) and disconnect and remove your battery. Remove your air filter, cover it with a plastic bag, and replace it, then block up and seal your exhaust and any drain holes it has with whatever comes to hand. Finally block off all engine, carburettor, fuel pump and oil tank breather pipes by folding and taping their ends. You are now ready for the crossing. If you have rope available, tie one end to the bike and the other to the far bank. Slowly push your bike across, positioning one person at the handlebars again up stream of the bike and one at the rear. If there are three of you then the third can pull on the rope or, if you have no rope, can pull the front of the bike. 

In the unlikely event of a drowned bike, don't panic. It's not the end of the world! If you follow the instructions outlined below you can salvage a bike that has even been fully submerged underwater. 

Take the tank off and drain completely. Refill with fresh petrol. 
Remove the sparkplug. 

Raise the bike to drain the water from the exhaust and cylinder. 
Kick the bike over a couple of times to clear all remaining water from the cylinder. 

Remove float bowl on the carburettor and drain. 

Remove the air filter and drain air box. Dry air filter. 

Allow the electric's to dry then spray with a water dispersing oil. 

Check engine oil, if a white-grey milky colour then replace with fresh engine oil. 

Replace the tank then check for a spark before replacing the sparkplug. 
Fire up the bike. 

Although very rare it is possible to experience what is know as 'hydraulic lock' when water is drawn into your engine. You know that this has happen because of the loud bang and sudden engine failure you experience.

What has happened is that the water your engine has sucked in, being non compressible, acts like having a lump of metal jammed into your cylinder. This usually destroys the piston and/or cylinder.

Generally a terminal problem this is one very good reason for you to be very careful when crossing water.