The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756.

[5] The French explorer and astronomer Nicolas Louis de Lacaille called it l’Hydre Mâle on the 1756 version of his planisphere of the southern skies, distinguishing it from the feminine Hydra.

The French name was retained by Jean Fortin in 1776 for his Atlas Céleste, while Lacaille Latinised the name to Hydrus for his revised Coelum Australe Stelliferum in 1763.

[7] Herman Melville mentions it and Argo Navis in Moby Dick "beneath effulgent Antarctic Skies", highlighting his knowledge of the southern constellations from whaling voyages.

[10] A line drawn between the long axis of the Southern Cross to Beta Hydri and then extended 4.5 times will mark a point due south.

Thought to be between 6.4 and 7.1 billion years old, this star bears some resemblance to what the Sun may look like in the far distant future, making it an object of interest to astronomers.

[7] Located at the northern edge of the constellation and just southwest of Achernar is Alpha Hydri,[17] a white sub-giant star of magnitude 2.9, situated 72 light-years from Earth.

[12] In the southeastern corner of the constellation is Gamma Hydri,[7] a red giant of spectral type M2III located 214 light-years from Earth.

It is a close binary system that consists of a white dwarf and another star, the former drawing off matter from the latter into a bright accretion disk.

[23] BL Hydri is another close binary system composed of a low-mass star and a strongly magnetic white dwarf.

A planet, Eta2 Hydri b, greater than 6.5 times the mass of Jupiter was discovered in 2005, orbiting around Eta2 every 711 days at a distance of 1.93 astronomical units (AU).

[37] The system is a complex one as the faint star GJ 3021B orbits at a distance of 68 AU; it is a red dwarf of spectral type M4V.

IC 1717 was a deep-sky object discovered by the Danish astronomer John Louis Emil Dreyer in the late 19th century.

Unusually, it has cohorts of globular clusters of three distinct ages suggesting bouts of post-starburst formation following a merger with another galaxy.

[41] The constellation also contains a spiral galaxy, NGC 1511, which lies edge on to observers on Earth and is readily viewed in amateur telescopes.

[12] NGC 602 is composed of an emission nebula and a young, bright open cluster of stars that is an outlying component on the eastern edge of the Small Magellanic Cloud,[44] a satellite galaxy to the Milky Way.