Lactococcus lactis subsp. lactis C 101910, isolated from lake water collected in Lake Motosu, Japan, was found to produce a bacteriocin-like inhibitory substance (BLIS) active against some Gram-positive bacteria. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the partially purified BLIS contained one antibacterial band approximately 2.5 kDa in size. When it was amplified with nisin-specific polymerase chain reaction (PCR) primers, a 320-bp PCR product was obtained. The PCR product was further sequenced and found to completely coincide with the sequences of nisin Z. This strain showed good performance in terms of growth and BLIS production when incubated in a simple broth at a low temperature. This is the first report to describe the characteristics of a lake-water-isolated strain of Lactococcus lactis subsp. lactis and to demonstrate that it produces a bacteriocin.