Between the 19 and the 23 of August Amsterdam hosted a huge marine event called SAIL Amsterdam. It’s held once every five years, and is most known for its tall ships (apart from hundreds of other ships). During the event they sail in loops around the IJ lake, giving the area a totally different look and attracting millions (yes, millions) of visitors.
For these days bridges over the IJ are open or even get dismantled to let the tall ships sail in.