Giant Mayflies emerge in peak numbers across New Hampshire

July 6, 2026

(Hexagenia limbata) reached their emergence peak this week, with 44 sightings logged across a seventy-mile stretch from Goffstown to Holderness on July 4 and 5. The timing is significant: these mayflies spend three years developing in stream sediment as burrowing nymphs, so their presence now signals that bottom oxygen levels have held steady enough to sustain a full aquatic life cycle.

Yet their emergence is a partial reprieve, not vindication. Within ten miles of the observation zone, fifty water bodies remain classified as impaired, and none is currently designated as fully supporting its intended uses. The giant mayflies are thriving where conditions permit — but the broader watershed is still struggling. Their success is a canary surviving in a cage, not a cage growing safer.

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June 28, 2026

are patrolling the ponds this summer, their iridescent bodies catching the light — a welcome sign of dragonfly activity in the region. Yet beneath that beauty lies a harder truth: all 47 of the water bodies assessed here are classified as impaired, none supporting their designated uses. The state lists ten of them under the Clean Water Act's impaired-waters inventory, a tacit admission that recovery is uncertain.Midsummer heat and stagnation are the immediate killers. Warm water holds less oxygen, and slow ponds become soup-thick with algae blooms — exactly the conditions that should favor dragonfly larvae, yet the oxygen crashes kill them before they can emerge. The Piscataquog's Abenaki name means "where deer drink," a name that still holds literal truth: deer still wade these shallows to drink, as their ancestors did. The water, though, is no longer fit for its original purpose. The skimmers are here; the system is not.

June 25, 2026

(Nannothemis bella) — North America's smallest dragonfly and a fastidious clean-water specialist — turned up here in early June. It is a striking sighting in this region, where all 47 assessed water bodies within the locale are impaired and none support their designated uses. The insects we see flying above the water are windows into what lives below: dragonfly nymphs spend years underwater developing, so their presence or absence is a direct statement about dissolved oxygen, chemistry, and the substrate conditions that support aquatic life.Recent dragonfly surveys in the area have logged roughly 22 observations across a dozen species over the past two months. The appearance of the Elfin Skimmer alongside this broader dragonfly activity creates a tension worth holding in mind — one small, particular species announcing that something here is clean enough, while the watershed as a whole remains listed as compromised. It suggests the margin between recovery and decline may be thinner than it appears.

June 25, 2026

Streamflow surged nearly 25-fold in two weeks, with the gauge jumping from a low of 157 cubic feet per second to 3,970 at peak—a gage height swing from 2.82 to 6.77 feet. The timing collided with mayfly emergence, when immature insects are most vulnerable to violent scouring. In a healthy watershed, such pulses are vital disturbance—renewal, migration cue, nutrient transport—but here the flood pulse simply moves the problem downstream.The water quality records tell the underlying story. Every assessed water body in the region is officially impaired—all 50 of them fail to meet their designated use standards. Only nine have made it onto the formal 303(d) list, meaning 41 are degraded enough to be tracked but not yet formally listed as polluted. The Merrimack at Garvins Falls Dam carries that formal 303(d) designation, a reminder that no volume of water washes away chemical or biological insult.A flood event in a truly functional stream renews the ecosystem; it scours filth, redistributes gravels, reconnects floodplains. Here, the disturbance merely amplifies an existing condition—moving contamination faster and farther, leaving behind the same degraded baseline.

More about Giant Mayflies

Giant mayflies emerge from the Hocking River

July 19, 2026

(Hexagenia species) emerged from the river this week in a quiet act of ecological recovery. Their nymphs spend years in the riverbed before crawling to the surface to metamorphose — a transition only possible in water clean enough and stable enough to support them through that long, vulnerable larval stage.The river still carries ammonia far above permitted limits, yet here the mayflies are. Their presence says something worth heeding: the water's capacity to support complex life is regenerating, even under the weight of upstream pollution. It's not a sign that the work is done — it's a sign that the system hasn't given up, and neither should we.