Spreck Rosekrans is an Economic Analyst at EDF.

As we hear cries of water wasting to the sea from the Bay-Delta, it is perhaps appropriate to remember that the Bay-Delta is a living estuary that needs water. Along these lines, we just received a blast from the past (courtesy of Jonas Minton) in the form of a 1980 letter (pdf) to then Governor Jerry Brown from Ph. D.’s lrwin Haydock (Marine Ecology) and Michael Rozengurt (Oceanography, Hydrology) that asserts it is an “inescapable conclusion that no more than 25-30 % of the natural flow can be diverted without disastrous consequences”.

Diversions have risen well beyond Haydock and Rozengurt’s threshold, to an average of 48% to date in the 21st century. It is important to remember that diversions not only include the exports that move water from the north part of California across the Delta to farms and cities in the south, but also water that is diverted upstream of the Delta and within the estuary as well. The upward trend of these diversions as California’s population has increased is unmistakable.

We do not know if Haydock and Rozengurt are indeed right, but we do believe that the system has been oversubscribed. We all acknowledge that we need to be as smart as possible about when and where we take water out of the system. But at some point, we need to realize that how much we take will matter if we want to maintain a healthy ecosystem.