The word Naga originates from India and it is a Sanskrit word where "Nag" means snake or cobra. Nagas (Tibetan: Lu) are a class of snake-like beings that dwell in a variety of locations ranging from oceans, rivers, lakes and other waterways or underground subterranean regions. Many Nagas can have extremely high realisation and they are considered to be protectors of the Dharma.
There are also Nagas who are not enlightened beings and they can easily cause obstacles for humans. Sickness and disease associated with the skin are often believed to be caused by displeased Nagas. This is one of the many reasons that bodies of water, such as lakes and rivers, are so highly respected and great care is taken to avoid pollution. Also, special Naga days are observed in the Tibetan calendar to help create harmony between both realms.