The "Bærum bassin" is a part of the Oslo fjord with quite many islands. Since the area is quite protected by the outermost islands, there is not so much circulation of the water masses there. The inner Oslo Fjord is rarely completely frozen, but the Bærum bassin freezes up completely almost every winter, to the extent that it's safe to walk on the ice during the winter time, they even make skiing tracks over the sea. This is of course also the last area to thaw up, it is often still icy in the middle of March or (like this year) even late April. I remember I was once very much surprised, enjoying a hot spring weekend day on my boat, "sea ice" wasn't on my mind at all, but when I tried to enter the Bærum bassin, it was full stop. What's moving so fast over there? Fetching my binocular, I discovered a human doing ice skating ...
The photos below was taken last Monday (almost a week ago), from Bærum - I didn't have time to check, but I'm pretty sure that Tuesday it was no ice anymore.
I had the Monday off due to night duties, and I needed to go from Sandvika to Bestumkilen to deliver the dhingy to a service. The gear wire had become broken (luckily it's a RIB and not a hard boat - I was going to pick up 
Here is Lille Ostsund, when I went out from Sandvika it was still a belt of ice stretching across the whole straight. (And it seemed to be even more ice towards the next straight, Snarøysund)
The ice was wet, soft and thin, so I sliced through very easily
Right at the outside of the Bærum bassin there was also small pieces of ice floating in the sea.
And a military minesweeper doing some practicing (they were putting some RIBs to the water when I was passing, on my return trip there was one RIB with people in military uniforms a bit on the distance from the mother ship, I have no idea what they were up to).
Now, the return trip, three hours has passed since the first photo - now there are only fragments of ice left in Store Ostsund. That's rather amazing! Me passing through it making an opening may have been a catalyzing it into dissolving into small fragments.
View towards Torvøya, Snarøya, Fornebu ... only some few pixels big on the scaled-down photo, but there is another sail boat on the photo, it was choosing the Snarøysund passage, probably still some ice left there, because he apparently used much more time than me.
It's not much visible on those photos, but there is actually quite much ice in the distance on both those two photos.
All photos available in better resolution on IPFS QmZ8Naiy4fCGDjTDC122kJaBDQzRPGuLJKnAh4bvAUymZX. License: CC BY-SA 4.0