Najas gracillima,[2][3][4][5] the slender waternymph,[6] is a submerged species of aquatic plant in the Hydrocharitaceae family.

It is native to China (Fujian, Guangxi, Guizhou, Hainan, Hebei, Hubei, Jiangxi, Jilin, Liaoning, Nei Mongol, Taiwan, Yunnan, Zhejiang), Russian Far East (Amur and Khabarovsk), Japan, Korea, Taiwan, Iran, Alberta, Ontario, Newfoundland, Nova Scotia, New Brunswick, the eastern United States (every state east of the Mississippi River except Florida, plus Minnesota, Iowa, Missouri and the District of Columbia).

It is also considered introduced and naturalized in France, Spain, Italy and California (Plumas and Tehama Counties).

[8][9][10][11] Najas gracillima is a small aquatic annual with branching stems.

[12] It lives in soft-water lakes and ponds with mud and silt bottoms, and appears to be sensitive to water turbidity, warming, and eutrophication.