Because Tower Bridge is the only bridge to open to allow tallish boats to pass through it.
Tower Bridge is raised to allow large ships to sail up the Thames.
London Bridge isn't an opening bridge. The only bridge in London which spans the river Thames and can open, is Tower Bridge. If a boat needs to have the bridge opened so that it can pass underneath, it has to book a slot in advance with the bridgemaster who will arrange to open the bridge at the agreed time.
putney
There wasn't a bridge on the site - just a ferryman with a rowing boat.
There isn't another bridge anywhere else in the world that looks anything like Tower Bridge so it is instantly recognisable. It is the only bridge over the river Thames that can be raised to allow tall-masted boats to pass under it. It is still possible for pedestrians to cross the bridge, even when it is 'open' to allow a boat to pass underneath.
A boat on the Thames
Yes, you can use the Thames River Cruise London Pass for a scenic boat tour along the Thames River in London.
You can boat on it, you can swim in it, sightseeing.
Yes
In January 2006 a juvenile female Northern Bottlenose Whale managed to swim from the North Sea up as far as Battersea Bridge in central London. It resisted all attempts to guide her back to sea and eventually died on a rescue boat as they headed back to the estuary.
No. Modern ships are so big that they would be too tall and too wide to pass through Tower Bridge and even if they could, they would be too big to turn round to get back again.
Oxford