The opening of the Lechmere viaduct across the mouth of the Charles in 1912 meant a dramatic reduction in the time it took trolleys to cross the river, from ten down to just three minutes - except when a cargo schooner came through and the trolleys had to stop for the viaduct's drawbridge to go up to let it through.
It's been decades since the drawbridge last opened, but remnants of it still remain. If you're driving past the Museum of Science, you can see it on the Boston side, right next to the car drawbridge that still does open on occasion to let pleasure craft into and out of the Charles. Look for the tower and metal gateways next to the Green Line tracks up there.
Boston Elevated trolley crossing the bridge on Aug. 8, 1912 (From the Boston City Archives):
MBTA inspector Tim Murphy, who has a keen interest in Green Line history (back in his operator days, he was the driver who'd entertain riders with history lessons over the PA), recently got a look inside the tower, where the bridge men used to watch over the then newfangled electromechanical machinery that would raise and lower the drawbridge's two sections - after first raising bumpers on the tracks to keep any errant trolley drivers from plowing ahead into the raised bridge.
He reports the bumpers were put in after the 1916 Summer Street Bridge disaster, in which a trolley just kept going even though the span was open, plunging into Fort Point Channel and killing 47.
Just in case the draws didn't go up or down by themselves, this box used to have two wheels attached that four men needed to turn to get the bridge back to where it needed to be:
Lots of gears:
The tower today:
The tower, viaduct and dam in 1912 (Via BPL):
But what were all those schooners (and large barges) doing going up and down the Charles?
Although the river today is largely the preserve of smallish boats, back at the turn of the last century, the Charles was very much an industrial river. Cargo ships - many still using sails - traveled as far inland as Harvard Square to unload their cargo. Coal barges in particular were a common sight on the river, traveling to the Broad Canal, where Kendall Square is today, to fuel a power plant there.
The ships continued their journeys even after the Charles River Basin Commission completed its work in building the Craigie Street dam - where the Museum of Science is now - to change the area just up from the river's mouth from a brackish tidal estuary into the placid, lake-like Basin we know today.
The goal of that project was mainly to do something about the stench from all the sewage dumped into the river by ensuring that mudflats on both sides, but especially on the Boston side, were always covered by water, rather than having them left exposed to the air at low tide (along with that came the installation of a big ol' sewer to carry wastewater past the mouth of the river and into the harbor).
But the commission also ensured a channel was carved out of the river bottom as far as Harvard Square (with a recommendation to eventually continue that up to Watertown Square) to allow for commercial ships to continue plying the river.
The commission voted itself out of existence in 1910, just as work was beginning on the Lechmere viaduct - which, like the Tremont Street subway in 1897, was meant to get streetcars out of the carriage and now car-crammed road it paralleled. But just like Silver Line buses crossing Chelsea Creek today, the trolleys still had to halt for river traffic, at least of the taller ships.
A cargo schooner in Lechmere Canal in 1904, from the Charles River Basin Commission annual report
In its final report, published in 1910, the commission reported that in 1909 there were 30 wharves along Broad Canal and 12 along Lechmere canal, with another 8 along the basin itself. Also:
One of the largest cargoes to pass through the Lock was 2,012 tons of coal, and another consisted of 537,000 feet B. M. of lumber.
In an article that focuses on salt-water "whaleback barges" that sometimes carried coal up the Charles, the Cambridge Historical Commission writes that in 1893 64 sailing vessels and 61 barges tied up at wharves in Old Cambridge (Harvard Square) and Watertown.
According to a US Army Corps of Engineers report, as late as 1939, some 421,279 tons of freight came into the Charles, including the Lechmere and Broad canals, including sand and fuel oil.
Murphy says the last time the drawbridge was actually raised was sometime in the 1970s. The bumpers meant to keep trolleys from careening into the Charles stayed in place until 2011, when they were removed as part of some viaduct renovation work.