This unusual small deer has a scientific name that means ‘unarmed water-drinker’, in reference to its lack of antlers and preference for marshy habitats. In the place of antlers, males have large upper canine teeth, that, in effect, are long, slightly curved tusks which protrude like fangs out of their mouths. The female is a little smaller than the male, and has much smaller canines. The Water deer's coat is rather coarse and thick, the color being reddish-brown during summer and more grayish during winter months, with whitish underparts. The young are darker brown and have white stripes and spots on the upper back.
Water deer occur in east-central China in the lower Yangtze Basin and in Korea. There are also small introduced populations in Great Britain and United States They inhabit areas with tall reeds, rushes along rivers, mountain areas and cultivated fields in tall grass. They also occur in open grasslands and swampy areas.
Water deer tend not to congregate in herds and are generally found in pairs or alone. A male will not tolerate another buck in close proximity and will defend its territory against all rivals. They will tolerate the company of a few females, which may accompany the male to seek food and rest within his territory. Water deer are most active during mornings and evenings, and during the day usually hide within dense vegetation. When disturbed, they will run with a characteristic series of leaps like a rabbit. Despite not being gregarious, these deer will alert each other to danger with brief shrill barking. The does make a soft peeping to call their fawns, and an injured deer makes a screaming wail.
Water deer have a polygynous mating system; a male mate with many females inside his own territory. The mating season is from November to January, with most births from May to July, following a gestation period of 170 to 210 days. Unusual amongst deer, females may bear up to 8 young, 1 to 3 being more common. After the birth, a female will often leave her normal range to becoming solitary. Fawns spend most of their first few weeks hidden in vegetation, coming out only when their mother visits to feed them. Fawns are weaned when they are about two months old. Males are usually sexually mature at five to six months of age, and females when they are seven to eight months old.
In their native habitat, Water deer are in serious decline due to habitat destruction and poaching. In some areas they are hunted, being considered an agricultural pest, and they are also hunted for their meat and for the use of semi-digested milk from the stomachs of unweaned fawns in traditional medicine. These animals are very sensitive to environmental change, and urban development and agriculture are important threats to its habitat. Much of their original range having been lost, the distribution of Water deer is continuing to decrease, and many populations are now quite small and fragmented.
According to the IUCN Red List, Water deer in Republic of Korea is said to be «moderately widespread», particularly along the west coast, as well as within the demilitarized zone between the two Koreas, but its population cannot be estimated. Specific populations have been estimated within China: 500-1,1000 deer in the coastal areas of Jiangsu; 1,500 deer in the Zhoushan Islands; around 1,000 deer in the Poyong Lake region, and an additional 500 individuals in Anhui. The British water deer population is about 1000 individuals. The IUCN Red List reports the decreasing trend for Water deer population and they are classified as vulnerable on the list on threatened species.