MORNING UPDATE: The Muddy River dropped below flood stage, even if barely, so Riverside service is running this morning - although river levels have started rising again (hourly river-level data).
LATER MORNING UPDATE: The Muddy River got all floody again, so the T put the dam back and stopped Riverside service.
Around 9 p.m., the MBTA blocked off the Fenway portal used by the Riverside line to prevent a recurrence of the 1996 floods that left Kenmore station submerged in 20 feet of water and required $40 million in repairs.
The move means Riverside commuters can expect delays tomorrow as they ride shuttle buses instead of trolleys between Reservoir and Kenmore, the T advises.
A federal monitoring station on the Muddy reported the normally docile river reached flood stage around 8:45 p.m. A T alert announcing the suspension of service between Kenmore and Reservoir went out not long after.