Understanding Sulfurs.

Back when I first started fishing the Delaware in the late 80's, the release from Cannonsville reservoir was 45cfs for ten months of the year. From June 15th until August 15th it was raised to 325cfs. Additional flow was dependent on reservoir spill, runoff from the tribs and releases to meet minimum flow requirements at Montague. Because the 45cfs flow bared a significant portion of the upper river there were very few caddis above Hale Eddy. The ten months of low flow limited the rivers carrying capacity of trout. It also allowed the river to become much warmer much earlier in the year.

How did this effect the sulfurs? During the 45cfs release era, the spring sulfurs (Invaria)  first appeared down in Callicoon sometime around mid May and worked steadily up the river system arriving in the water above Hale Eddy as early as the 10th of June. I often witnessed massive spinner falls usually around the 20th of June.. Back then I was unaware of the two different species of sulfurs but there were sulfurs above Oquaga in late June and they continues throughout the summer.

The releases on the WB have been reviewed and modified numerous times since then. The present day FFMP release program was started in 2007. The FFMP plan has, at least in my opinion, been the single biggest contributor to the improved fish carrying capacity of the river system. Gone are the draconian low winter flows that drastically reduced up river fish and insect populations. The FFMP is complicated and need not be discussed in detail here, just know that as long as there is a good supply of water the releases will remain far greater than under past regimes.

How does this affect the upper WB sulfur hatch? I'm not a marine biologist and my observations are just that, the reasons for the changes may be far different than what I think. That said, the releases from Cannonsville under the FFMP are now 500 cfs. The water in the upper Delaware is much colder than it use to be. The cold water  has probably slowed and perhaps even diminished the Invaria hatch in the water above Hale Eddy. I don't know what water temps the Invaria thrive in and I don't know if that species of sulfur is actually happy in tail waters. The summer sulfur (Dorthea) is the little one that proliferates the "Sulfur Zone" in July and August". They are clearly a tail water fly. Because I never distinguished between the two species my old log books show sulfurs appearing up river around June 20. Probably the Dortheas never got going that early. Under the FFMP, Dortheas are normally hatching with regularity by the end of the first week of July. Before the FFMP the hatch often continued into September, under FFMP the hatch seems to taper off near the end of August. The increased release under the FFMP results in the water beneath the thermocline being used up sooner and as the temperature of the release water rises the sulfur hatch wanes.

This year the Invaria hatches seem to be less prolific than in years past and as a result the WB has suffered a more prolonged doldrum period. It is quite possible that the Dortheas may also be a bit tardy in making their up river appearance. Why? Smoke from forest fires in Canada together with more cloudy weather during the past three weeks have resulted in cooler water temps in the "Sulfur Zone". Sulfurs like low 50's water temp and most days the water temp up in Deposit has stayed in the 40s. The plus side in this equation is that fish have remained in the freestone portions of the river system for what is now about three weeks longer than usual. This spreads out the fishermen and takes the pressure off the upriver fish. Be ready, the pendulum will probably swing soon.