River Hills

The past 30 days at Cahokia Airport show mean daily high of 80.8°F, 6.8°F above the normal of 74°F. This sustained warmth above normal continues a trend seen 30 days ago at the start of this monitoring period and maintains conditions favorable for increased evapotranspiration and drying of surface fuels.

Mean daily high temperatures at Cahokia St. Louis Downtown Airport have run 6.8°F above the 1991-2020 normal over the past 30 days, with mean daily lows 6.3°F above normal. This sustained warmth significantly exceeds typical late September and October conditions for the region.

A Giant Floater mussel was observed at Pontoon Beach, IL on October 8, 2026. This native freshwater bivalve indicates the presence of harder substrate suitable for mollusks in the watershed, though freshwater mussels are among the most imperiled groups in the United States.

St. Louis County remained at D0 (Abnormally Dry) conditions for 100.00% of its area for the week of 2026-10-13 to 2026-10-19, persisting unchanged for five consecutive weeks since early September. These sustained low-moisture conditions stress amphibians and water-dependent insects that breed in regional wetlands.

American Bumble Bee was observed on 2026-10-19 at Missouri Botanical Garden, the most recent sighting in the past month. This federally threatened species continues to forage in local gardens as fall approaches, though the 11 total observations in 30 days reflect limited activity as temperatures decline.

A Scarlet Tanager was confirmed near Des Peres on 2026-10-11, in the latter phase of fall migration through Missouri. Males molt from brilliant scarlet into dull olive-yellow by fall, and the species departs for its South American wintering grounds by mid-October.

A Yellow-bellied Flycatcher was confirmed at Tower Grove Park on 2026-10-14, representing ongoing fall passage of this small flycatcher breed in Canadian boreal forests. The species passes through the region in fall, foraging on small insects as it migrates to Mexico and Central America.

A Blackburnian Warbler was confirmed at Tower Grove Park on 2026-10-14, part of the species' tail end of fall migration through Missouri. This small insect-gleaning warbler breeds in northern boreal forests and winters in Central and South America, passing through the region during September and early October as it heads south.

River des Peres is listed as impaired under the Clean Water Act, requiring a cleanup plan (TMDL). The Mississippi River segments in Illinois near River Hills are also listed as impaired, with assessments completed in the current 2026 cycle. These listings indicate state assessment of the waters' failure to meet designated uses.

Silver carp (Hypophthalmichthys molitrix), a federally threatened invasive species, were recorded at Lock and Dam Way in Alton, IL on September 16, 2026 and at other locations in August and September. The species is native to Asia but widely farmed globally; escapes from aquaculture establish feral populations that outcompete native fish through filter feeding.