Telmatrechus is an extinct heteropteran genus in the water strider family Gerridae which is solely known from Early Eocene sediments exposed in western North America.

Fossils of Telmatrechus are found in early Eocene, Ypresian age lacustrine deposits in two areas of Western North America.

T. stali has only been reported from an outcrop of the Allenby Formation on the North Fork of the Similkameen River near Princeton, British Columbia.

The older Fossil Butte sediments are considered Early Eocene, and overlap the Okanagan Highlands Ypresian dating.

Based on a group of four fossils from the recently discovered Green River Formation outcrops at Twin Creek, Wyoming.

[2] The final species was not named until 1910 when Austrian paleontologist Anton Handlirsch was loaned a group of British Columbian fossils for description.

While working on the fossils, he formed the opinion that Scudders genus Telmatrechus was "not well founded" and indicating that he considered T. stali as the type species.

A comprehensive review of the know fossil water-striders and their close relatives was conducted by Nils Møller Andersen (1998), in which he addressed the placements of all three species in question.

[1] The validity of the genus was again questioned a decade later in Jakob Damgaards 2008 evaluation of Gerromorpha evolution and fossil history.

Taking a middle of the road approach between Scudder and Handlirsch, he noted that the three species shared a number of characters with the remigis-species group in genus Aquarius.

This feature was questioned by Andersen, who suggested the profile of the abdomens was a preservational artifact, and the laterotergites on the sides were simply missing.

Scudder described the coloration of the specimens as fairly uniform "brick" tone, with a course or rough exoskeleton texture on both head and thorax.

The head is only visible in side view, but appears to be rounded in outline rather then the triangular of T. defunctus and larger then in T. parallelus with an estimated length of 1.5 mm (1⁄16 in).

This was interpreted as the remains of full wings, which only extended across half the abdominal length and the longest of the lines being from the claval suture.

The highlands, including the Early Eocene formations between Driftwood Canyon at the north and Republic at the south, have been described as one of the "Great Canadian Lagerstätten"[19] based on the diversity, quality and unique nature of the paleofloral and paleofaunal biotas that are preserved.

The highlands temperate biome preserved across a large transect of lakes recorded many of the earliest appearances of modern genera, while also documenting the last stands of ancient lines.

[19] The warm temperate highland floras in association with downfaulted lacustrine basins and active volcanism are noted to have no exact modern equivalents.

[20] Both Okanagan Highlands formations represent upland lake systems that were surrounded by a warm temperate ecosystem[21] with nearby volcanism[19] dating from during and just after the early Eocene climatic optimum.

The highlands likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable.

The CLAMP results after multiple linear regressions for Princeton gave a mean annual temperature of approximately 5.1 °C (41.2 °F), with the LMA giving 5.1 ± 2.0 °C (41.2 ± 3.6 °F).

A bioclimatic-based estimate based on modern relatives of the taxa found at each site suggested mean annual temperatures around 13.1 ± 3.1 °C (55.6 ± 5.6 °F) for Princeton and 15.0 ± 0.6 °C (59.0 ± 1.1 °F) for Quilchena.

At the same time in the early Eocene the Mississippi embayment extended much further north and westwards, placing the gulf coast shoreline much closer to the Green River basin.