If one particle makes a current, there are lots of particles that hit the Earth at energies much more than 0.98c, most famously the "Oh my god particle"
If you have many particles travelling at these speeds you don't have a river, more a beam, or a jet or particles. These are produced by active accretion disks around black holes.
In this combination image from Nasa (the background is a visible light image from hubble, the pink lobes are from the VLA, a radio telescope), an active radio galaxy is producing two jets, that are much longer than the size of the galaxy. These consist of particles that have been accelerated by the black hole's gravity and shot into space. A ship would find it hard to use the energy in these jets. Particles travelling at close to the speed of light are high energy radiation. A space ship unlucky enough to pass unprotected through the beams would be irradiated. I haven't done the maths, but the dose would probably be enough to kill anyone on board. It's hard to extract useful energy from anything so violent.
However if you are looking for random currents of charge, curving between the stars, and interstellar sailors tacking and jibing betweent them, you may be out of luck.