What's living on the river bottom โ reach by reach (2025) and across the last decade (2016โ2025). From the Foundation's macroinvertebrate sampling program. The nymphs counted here are next season's hatches.
The three aquatic-insect orders anglers live for โ and the ones biologists grade water quality by:
These bugs are sensitive to pollution and warm, silty water, so the % of all bugs that are EPT is a quick health grade: under 30% = marginal, over 50% = excellent. The bonus for fishermen: EPT bugs are exactly what you tie on โ high %EPT means clean water and good hatches. The Henry's Fork runs ~53%.
Total invertebrate density (individuals/mยฒ), upstream โ downstream.
% mayflies, stoneflies & caddis. Above 30% = good water; the Henry's Fork is double that.
Density (individuals/mยฒ) of the bugs anglers actually fish โ by site.
Pale Morning Dun (Ephemerella) nymph density โ the river's signature hatch.
Giant salmonfly (Pteronarcys californica) nymphs โ Box Canyon/Ashton reaches.
The famous Ranch hatch. Best modern years: 2025, 2017, 2020. Note: bug numbers don't track perceived hatch quality.
Watershed-average %EPT by year โ a steady improvement in the bug community.
Watershed average. Drifting down ~4%/yr โ midges/non-insects replaced by EPT bugs.
By far the most PMDs of any site โ but the one reach showing a concerning decline.