Hi,
Are you referring to the rookery at the old growth stand of willows at the Lower Klamath, CA side?
If so, even though I haven't been there myself, I would venture a good guess that the rookery failed due to lack of food. Nesting requires "easy" accessible food sources, and with the lack of wetlands, which the egrets and herons are adapted to, they likely abandoned the area and went where they don't have to fly more than 10 miles one way to get food easily, or may not nest at all this year
There are rookeries in the Upper Klamath area, but none that are easily seen or observable like the one you mentioned along the tour route. Hopefully the Lower Klamath can return to its former self as an impressive wetlands area in the near future, like next year.
Kevin Spencer
Klamath Falls
Sent from my Verizon LG Smartphone