Hydrovatus seminarius, is a species of predaceous diving beetle found in India, Bangladesh, Bhutan, Myanmar, Nepal, Pakistan, Sri Lanka, China, Indonesia, Japan, Laos, Malaysia, Taiwan, Thailand, Vietnam and Australian region.

[1][2] This large species has a typical length of about 2.4 to 2.8 mm.

[3] Head between eyes narrowly margined.

In male genitalia, the apical part of penis is evenly curved ventrally.

Male stridulation apparatus on metacoxal plates along suture close to metathorax.