The Super-Kamiokande is a 50,000 ton water Cherenkov detector  underground. The primary uses for this detector in Japan in addition to neutrino observation is cosmic ray observation as well as searching for proton decay. In 1998, the Super-Kamiokande was the site of the Super-Kamiokande experiment which led to the discovery of neutrino oscillation, the process by neutrinos change their flavor, either to electron, muon or tau.
The Super-Kamiokande experiment began in 1996 and is still active. In the experiment, the detector works by being able to spot neutrinos by analyzing water molecules and detecting electrons being removed from them which then produces a blue Cherenkov light, which is produced by neutrinos. Therefore, when this detection of blue light happens it can be inferred that a neutrino is present and counted.