At the November 21, 2014 public meeting in Kernville regarding the Isabella Dam project, the Corps posted the following slide (dated November 17, 2014) indicating the pool restriction would be in effect from late 2020 until June 01, 2021:

However, the Corps' Final Environmental Impact Statement, released in October 2012, states the pool restriction will be in effect during "a four-to-six-month window from Fall 2020 to early Spring 2021." (Final EIS at pp. 2-5, 2-10, 2-13, 2-24, 3-16, 3-30.) 

Spring begins in late March, so KRB analyzed the historical April 01 storage data for the Isabella reservoir. The result is that over the last 50 years, storage in the reservoir on April 01 has averaged 204,827 acre-feet.

If, contrary to November 17 slide above, "early Spring" is when the Corps is targeting to lift the pool restriction, then around April 01, 2021 storage in the reservoir will be at 72,237 acre-feet, or less.

The reservoir has a storage minimum. 30,000 acre-feet are required to remain in the reservoir for lake recreation. Thus, while the April 01 average storage available for river release has been 174,827 acre-feet, on or around April 01, 2021 only 42,237 acre-feet will be available. The pool restriction accordingly limits useable water to 24% of the historical average.

Fast forward to the summer of 2021. The watermaster has never released boatable flows with storage in the 72,000 acre-feet range. There is no guarantee the watermaster will release inflows from that season's snowmelt at boatable levels during the summer of 2021, as opposed to using those inflows to fill the reservoir. There may not be sufficient inflows to release at boatable levels should the Southern Sierra experience drought the previous winter. And, of course, project delays could keep the pool restriction in force beyond early Spring 2021. 

KRB continues to believe the Isabella Dam project's pool restriction will unavoidably damage the 2021 summer boating season on the Kern below the reservoir, and the Corps should mitigate that damage with a regime of "bubble" releases.