This video from Britain is called Harbour Porpoise Species Identification.
Translated from Dutch Vroege Vogels radio:
Wednesday, August 3, 2016
The young harbour porpoise which was spotted last week in the canals of Den Helder, is swimming through the channel along the N9 motorway further south into North Holland province. The last time the about a meter long mammal was seen was near Alkmaar, said a spokeswoman for the SOS Dolphin Foundation on Wednesday.
The animal may also swim south to Amsterdam. A porpoise is a toothed whale species that belongs in sea water. “It is in fresh water where there is not enough fatty fish, making it weaker every day”, said the spokeswoman.
UPDATe 14 August 2016: same porpoise probably found dead near Krommenie: here.