As this really old post has still a good ranking at Google for sealock IJmuiden, I will update it in regular intervalls.

Link for the Webcam from „Port of Amsterdam“:
https://www.portofamsterdam.com/en/discover/experience-port/webcam-ijmuiden This webcam is showing an moving overview of the IJmuiden harbour, starting at the entrance, via Fort Island over Tata Steel Factory and the Felison Terminal (Mostly with King or Princess Seaways and Emma of course).

There are some more webcams at IJmuiden:

View to the harbour entry direction North Sea:
https://www.webcam-havenijmuiden.nl/pages/cameras/havenmond.php This camera is located at Seinpoststelling. A very nice place to stay a few days an watch ships. 

Moveable camera direction harbour and Sluis:
https://www.webcam-havenijmuiden.nl/pages/cameras/haven.php

The 360° moving camera at Marina Seaport gives a very good overview over the Beach, the marina and the entry to the north sea canal:
https://webcam-marinaseaport.nl/

The Beach at Wijk/Nordpier from the Timboektoe https://www.timboektoe.org/webcam/ and from the Aloha https://alohabeach.nl/webcam-weer/

Old Post for reference and the deep links….:

Die Webcam an der Schleuse (Sealock) in IJmuiden funktioniert mit dem originalen Link, der auf der Seite https://www.portofamsterdam.com/en/webcam-sealock angegeben ist, leider nicht mit Chrome. Safari, und Internet-Explorer zeigen das Kamerabild an.

Für Chrome funktioniert aber folgender Deep-Link wunderbar: Webcam Zeesluis-IJmuiden.

Der funktionierende Link für die Kamera im Hafen Amsterdam an der Central Station ist: Webcam of the port, at Central Station in Amsterdam