The river Vecht, that runs from the Rhine and Utrecht to the former Zuyderzee, has been a main traffic route for thousands of years. During all that time, people have thrown stuff in it, lost things, and over time, scores of boats did sink here.
And also, the ever slower flowing water deposited gigantic quantities of mud. With the river level being structurally higher than the land on most places, something had to be done to improve the water circulation.
Recently, and for the first time ever, the whole river has been dredged, and cleaned. That objects of the past millennia would be found was logical and expected. But the amount and quality surprised everybody.
In 2014, an exhibition with a first selection was on display in the city hall of Weesp, and later travelled to other towns along the river.
The dredging of the river has taken years, also because of delay due to World War II bombs and dumped ammunition. See 1945 bombs.
The job should be finished completely in 2015. By that time about 2.5 million cube meters of mud will have been dredged, and removed by barge to other locations.
Cleaning and studying all the new finds will also take many more years.
Link to the regional Water Board, responsible for the river dredging and the exhibition : www.agv.nl.
On that website, also a nice downloadable flyer in English on Dutch water management in general.
More on Dutch Water Boards : 700 years of tradition down the drain ?