this has nothing to do with upstream reservoirs or horsetooth. the water is still up in the canyon, at about 130 cfs from the main/ n. fork confluence down through picnic rock. it looks like about 40 from the n. fork, which leaves about 90 coming down the main poudre. what is happening is diversion of the water before the gage at the canyon mouth.
you know all the reservoirs you see on aerial photos and topo maps that are between ft. collins and wellington? well, its time for the canal companies to fill them up for the irrigation season before farmers start calling for their senior priority direct flow rights. one of the diversions they use to fill these is the low-head dam just below the picnic rock parking area, but still above the gage, and that ditch is now full of water, probably about 100 cfs. there is one other diversion above that one, that is between filter plant and bridges, which is not yet diverting. when it does start, the gage will likely drop again, but the bulk of the runs, excluding filter plant, will not be affected.
long story short, if +/-130 cfs was enough for you, filter plant still has it, and the runs above that still have +/-90 cfs, just like they did before the gage dropped.
p.s. the rock is about 0.1 ft.