Winter Swimming, Krasnoyarsk, Siberia

One way that the hole is maintained at regular ice swimming places is with a pump that forces the water to circulate under the hole, preventing ice from forming. Small ice-holes can also be kept open by keeping a lid over the hole to prevent ice forming.
Most ice swimming places also use a specific heated "carpet" going from the locker rooms to the ice-hole, both to make walking to the hole more pleasant and for safety as otherwise the water dripping from returning swimmers would freeze and create a dangerously slippery surface to walk on.