The "Harry Kim wormhole" was the name that Tom Paris proposed petitioning the Federation Astronomical Committee to officially designate the wormhole discovered by Harry Kim in the Delta Quadrant in 2371.
Although exhibiting the usual properties of a wormhole, including verteron emanations and tunneling secondary particles, it was discovered that the wormhole was too small to travel through, having a width of approximately 30 centimeters. Unable to trace its subspace bearing, the Voyager crew sent a microprobe into the wormhole, where it encountered extremely dense microscopic gravitational eddies and extremely constricted spatial dimensions. Kathryn Janeway suggested that this was because it was in an advanced state of decay, and that it had been collapsing for centuries. Kim tried to determine the location of the other end of the wormhole by extrapolating the verteron exit vector, but was unable to due to an unusual phase variance in the radiation stream.
While traveling through the wormhole, the microprobe became mired in a gravitational eddy, becoming lodged in the wormhole. The Voyager crew was able to use the microprobe as a communications relay, contacting the Romulan science vessel Talvath in the Alpha Quadrant. The vessel's captain, Telek R'Mor, was able to beam to Voyager using the probe as a relay. Scanning R'Mor, Lieutenant Tuvok found that he was exhibiting clear signs of temporal displacement, and discovered that the wormhole was a rift not only in space, but in time as well, connecting to twenty years in the past.
Realizing that they could not beam the crew through the wormhole due to the effects it would have on the timeline, they were forced to abandon the plan, and transported R'Mor back to his ship. (VOY: "Eye of the Needle")