Based on the question as it is now, a sort of solid energy barrier to block water, you would need a cold plasma shaped by magnetic fields to act like a barrier.
Plasma is just ionized gas, such as evaporating wax as it's burning at the top of a candle. It's quite easy to control the flow of plasmas within electromagnetic fields.
To ionize something, either add electrons or strip away electrons. A high voltage antenna such as a tesla coil can ionize air quite easily, making spectacular arcs of lightning fly out. The process goes on in fluorescent light bulbs, neon signs, all TVs except for the LED based ones, etc., and as I said earlier, from many chemical reactions that cause things to burn.
What is beyond the realm of physics, though, is a way to keep a gas ionized while it's in contact with water. Since non-purified water is an excellent conductor, as soon as a plasma touches it, the plasma is grounded out, bringing the number of electrons back to a neutral state.
Since your gas is in a neutral state, it's not a plasma any more, so can't be directed by magnetic fields.
This is where you'd use some handwavium: a gas that stays ionized even when in contact with an excellent conductor.
Alternatively, you could keep on bombarding the seas with newly ionized plasmas accelerated towards the water by vast arrays of plasma "guns" (which would resemble a gun in much the way a wide nozzle power washer resembles a gun; it's not a single kinetic round travelling in a ballistic arc, it's a steady stream of particles spraying out and expanding out in the same general direction) but then it's the wind pushing the water back, not any sort of "energy barrier." You might as well just get tons of fans to blow the water; as it would be far more efficient and just as hilarious.
If you want to avoid handwavium, though, just set up inflatable dams like they have protecting some inland lakes from storm surges in the Netherlands.