This is a small coenagrionid damselfly characterized by striking sexual dimorphism and remarkable female polychromatism. Adult males typically reach a total body length of 25 to 31 millimeters, displaying a mostly black abdomen with a prominent, vibrant bright blue patch located on the eighth abdominal segment. The male´s thorax features distinct neon green or sky blue antehumeral stripes that stand out against the adjacent dark bands. Females exhibit a fascinating polymorphic coloration, consisting of andromorphic individuals, which closely mimic the blue and black coloration of males, and gynomorphic individuals, which present more cryptic tones such as brown, dull orange, or olive green. Both sexes possess hyaline, membranous wings, with the males having a distinctive bicolored (greyish-white) diamond-shaped pterostigma on their forewings, serving as an essential diagnostic feature to identify Ischnura fluviatilis in the field.

Geographical distribution: This taxon is widely distributed throughout the southern half of the Neotropical region. Its geographic range extends across central and southern Brazil, covering the entirety of Paraguay and Uruguay, and reaching into the temperate and subtropical zones of Argentina, with verified populations also recorded in central-northern Chile. It exhibits remarkable latitudinal adaptability, successfully colonizing diverse river basins and wetlands from sea level up to elevations of approximately 1500 meters above sea level.

Habitat: It primarily inhabits lentic and slow-moving lotic freshwater environments. These habitats include shallow lagoons, marshes, swamps, and the quiet margins of slow-flowing rivers. The presence of dense emergent and floating aquatic vegetation, particularly macrophytes of the genera Eichhornia and Pistia, is critical, as these plants provide essential microhabitats for nymphal development, perches for adults, and substrates for egg deposition. It is a highly resilient species capable of tolerating moderate levels of water eutrophication and anthropogenic environmental disturbance.

Feeding: This insect is strictly carnivorous throughout all stages of its life cycle. In the aquatic nymphal stage, it behaves as an opportunistic sit-and-wait predator, preying on small aquatic invertebrates such as cladocerans (water fleas), copepods, dipteran larvae (especially chironomids), and tiny crustaceans. Upon emerging as flying adults, they become agile aerial predators, capturing prey mid-air or gleaning them directly from vegetation. Their diet consists of mosquitoes, midges, aphids, and other soft-bodied small insects that frequent riparian zones.

Behavior: It exhibits diurnal activity patterns, with peak flight and interaction times occurring during hours of maximum solar radiation. Males are territorial and defend small perching territories on floating leaves, where they actively scan for receptive females and aggressively drive away rival males through swift, hovering chase flights. Their flight style is generally low, fluttery, and restricted to short distances, staying just centimeters above the water surface or shoreline vegetation to avoid predation by larger dragonflies and insectivorous birds.

Reproduction: The reproductive process begins with male courtship leading to tandem formation and the subsequent wheel position characteristic of odonates. Following copulation, which lasts for several minutes, the female carries out oviposition, typically without the male in tandem, though he may guard her from nearby perches. The egg-laying process is strictly endophytic, meaning the female uses her serrated ovipositor to cut slits into the living tissues of floating or submerged aquatic plants, depositing her elongated eggs individually inside the plant stems or leaves. After an incubation period, aquatic nymphs emerge and undergo several developmental instars before climbing out of the water to undergo their final metamorphosis into winged adults.

Conservation status: It is currently categorized as Least Concern (LC) on regional assessments and global checklists of Neotropical Odonata. This status is justified by its extensive geographical distribution, high population density, and notable adaptability to human-altered aquatic systems. Nevertheless, localized threats persist, primarily driven by the destruction of wetlands, chemical pollution from agricultural runoff, and the drainage of small water bodies for urban development and agricultural expansion.