San Francisco Peninsula

Juvenile white sharks, which typically measure between four and ten feet in length, are moving northward even into central California and may stay in nearshore areas for longer than usual during the marine heatwave and El Niño conditions. Emergency beach fishing regulations adopted this summer now prohibit certain large-hook and metallic fishing gear from Pigeon Point in San Mateo County south to reduce dangerous encounters between hooked sharks and swimmers.

Yellowfin, bluefin, and albacore tuna have all shown up off the California coast in large numbers in 2026, along with more infrequently seen fish such as wahoo, striped marlin, bullet tuna, and dorado. A marine heatwave has increased ocean temperatures this year, drawing warmwater and tropical fish species farther north than usual into California coastal waters.

California fuchsia was observed in bloom on September 27 on the Peninsula. This native perennial is notable for bright scarlet flowers in late summer and autumn, with its peak flowering running through early October as temperatures cool into fall.

Evening Grosbeaks were reported in elevated numbers on 2026-10-02 across the Peninsula, with 60 separate reports including a high count of 34 at Hawk Hill, flagged as regionally notable. This finch family member tracks fall migration pulses driven by day length and seed availability across western habitats.

Monarchs were recorded across the Peninsula and Bay Area on 2026-10-02, with 171 observations through iNaturalist in the past 30 days. The western monarch migration to coastal California overwintering sites typically begins in August and runs through November, with colonies forming from October through February. Early October passage indicates the migration is on schedule.

Early September is the part of the year the California red-legged frog (Rana draytonii) spends away from water. Breeding ran from November into April. By now most adults have left the ponds and moved into the surrounding hills, sitting out the dry months under rocks, in leaf litter, in animal burrows, or down in the cracks of a pond bottom that has already dried. A frog can travel a mile overland in wet weather and settle two miles from where it bred. The sightings logged this month are single frogs in refuge, not a gathering at any one pond. It is the largest frog native to California, up to four and a half inches from snout to rump. The back is reddish brown to olive with irregular dark blotches. A raised ridge of skin runs along each side from behind the eye to the hip. A dark mask crosses the face above a pale stripe on the upper lip. Turn one over, or catch it mid-leap, and the belly and the undersides of the hind legs are washed in red; that is the name. Young frogs may show yellow there instead of red, with heavier spotting on the back. Two other frogs share these hills. The Sierran treefrog is a fraction of the size, two inches at most, with toe pads and no side ridges, and it owns the loud two-part ribbit of the movie soundtracks. The red-legged frog's own call is a low, stuttering grunt that carries poorly. The American bullfrog is the one to look at hard. It is bigger, green about the snout, with a very large eardrum behind the eye, and it lacks both the side ridges and the pale lip stripe. Its call is the deep jug-o-rum. The bullfrog matters for more than identification. It was introduced to California, it breeds over a longer season, and its tadpoles eat red-legged frog eggs and tadpoles. In one study, red-legged frog larvae sharing a pond with bullfrog tadpoles survived at under five percent, against thirty to forty percent where bullfrogs were absent — the proposed mechanism is direct predation by bullfrog tadpoles and juveniles on red-legged frog eggs and larvae, plus competition for the same shallow-water habitat. Not every study finds that pattern; some point out that bullfrogs tend to turn up where ponds have already been altered, so the two effects are hard to pull apart. Bullfrogs were logged through the same weeks this summer around Mill Valley and Lake Lagunitas, in the Marin hills. iNaturalist hides the exact location of red-legged frog records, so whether the two share any particular pond is not something the records show. What the red-legged frog needs from a pond is specific. Eggs go into shallow water at the vegetated edge in loose clusters and hatch within two weeks. The tadpoles then take three and a half to seven months to become frogs, so a breeding pond has to hold water from winter into summer. It also has to stay cool. The frog cannot survive water above 29 degrees Celsius (about 84 F), and ponds with willows and cattails standing over deep water do best. The emergent plants do double duty: they hide tadpoles from herons and fish, and they warm the shallows enough to grow the algae the tadpoles feed on. The species is listed as threatened under the federal Endangered Species Act, and mapped critical habitat overlaps the Peninsula. Anyone who finds one of these frogs this fall, under a board or beside a seep well away from open water, is seeing the non-breeding phase that can take up as much as eleven months of its year.

A California buckeye along the Peninsula is doing something it has no business doing in late August: it flowered on the 27th, pale pink-and-white spikes opening even as its own leaves color and drop and last spring's fruit hangs ripe on the same branches. Three life stages, all showing on one tree at once. To understand why that's strange, it helps to know how this species normally runs its year. Buckeye is usually the first tree on the Peninsula to leaf out each spring, often by February, and one of the first to shut down again, dropping leaves as early as July in a dry year. That early exit isn't decline, it's strategy. Most deciduous trees drop their leaves on a calendar cued by shortening days and falling temperatures, but buckeye is drought-deciduous: it reads soil moisture instead, and pulls the plug on photosynthesis before the dry Mediterranean summer can pull the water out of it by force. A tree that manages its own dormancy on that kind of internal trigger, rather than an external clock, is also a tree with more room to misfire, and an occasional stray environmental nudge can push it into throwing a second, out-of-cycle bloom well after its main season has closed. What makes this particular bloom worth watching is who showed up for it. An Anna's hummingbird was logged working the same stretch of Mission Creek today, and buckeye's tubular flowers are built almost exactly for that bird: long and narrow, favoring a hovering, long-billed visitor over a crawling insect. Unlike the ruby-throated and rufous hummingbirds that clear out of California by fall, Anna's hummingbird stays on the coast year-round, so a flowering buckeye in late August isn't dropping nectar into an empty season. There's a resident pollinator on the landscape to use exactly what it's offering. California buckeye carries no special conservation status, so none of this is a red flag. It's simply a small, precisely timed piece of plant physiology showing its hand on one tree, the kind of detail that only stands out because the buckeye's usual calendar is so well known.

Of the thousands of permitted dischargers tracked across the San Francisco Peninsula and Bay watershed this period, exactly one has landed on EPA's list of Significant Non-Compliance: the Treasure Island Wastewater Treatment Plant, which discharges directly into San Francisco Bay. That designation is EPA's own threshold for regulatory priority, reserved for violations judged serious enough in scale or duration to demand attention. The specific effluent parameters behind the listing weren't detailed in this pass, so the exact magnitude of the exceedance isn't clear, but standing alone on that list is itself the signal worth noting. The plant's troubles fit its known condition. It's aging, seismically vulnerable, and prone to combined-sewer-overflow risk whenever heavy rain overwhelms its capacity, which is precisely why it's now mid-construction on a $369 million federally financed rebuild. Water-quality gauges near Pier 17 and off Alcatraz's northeast shore currently read within normal late-summer ranges for temperature and dissolved oxygen, but with only three readings logged in the past month at each station, that record is far too sparse to say anything meaningful about conditions right at the outfall itself. Baykeeper tracks Bay pollution discharges and is a useful point of reference for anyone following this facility's compliance record as the rebuild moves forward.

Scarce Striped Grass-veneer (Ancylolomia tentaculella) turned up today in San Francisco County — a European moth that has been quietly establishing itself across California over recent decades. This is the first iNaturalist record within 50 kilometers in the past year, though the identification is still awaiting expert confirmation and may yet shift. The sighting makes ecological sense: this moth tracks disturbed, grass-heavy habitats—roadsides, parks, urban margins—which the peninsula offers in abundance. The larvae feed on grasses, and the species tends to slip in unnoticed until populations are already well-settled. Unlike flashier agricultural pests, Scarce Striped Grass-veneer moths rarely trigger alarm bells until ecosystem surveys catch them in the record. Worth flagging while the identification is still open, especially given how much of the habitat here is already shaped by human disturbance.

Humpback whales (Megaptera novaeangliae) are feeding in the waters just off the Peninsula right now — 44 occurrences recorded in the past two months mark this as the peak of their annual summer residency here. They arrive drawn by the cold, anchovy-rich upwelling that the California Current drives along this coast each summer, a seasonal pulse of abundance that Coastal Miwok and Ohlone peoples knew intimately across millennia of living alongside these waters. Unlike the gray whales seen foraging in the Bay this spring under conditions of ecological stress, humpbacks belong in these waters in July. The northeast Pacific population has recovered substantially since the end of commercial whaling, and their strong summer showing is one of the clearest signs that the offshore food web, for now, is still functioning.