Our Bay: This Week's Take: Tipping points for the bay

In the upper Chesapeake Bay, cutting pollution has lagged well behind goals scientists say are needed to restore the estuary.

Yet across thousands of acres there, all-important underwater grass habitats have exploded in recent years to levels not seen in half a century.

Downstream, throughout much of the bay's main stem, excessive pollution levels have held fairly steady during recent decades.

Yet deepwater "dead zones," massive volumes of water with too little oxygen for aquatic life, have steadily worsened and expanded there.

And another wrinkle: Just in the last couple years there are tantalizing...