I can't believe my own eyes, someone else is posting about The Long Dark. This must be the best day in my Hiver career.
Something that connects the different regions that we are going to travel through are the train tracks.
Excuse the lame pun, but always keep track on those tracks. When you get hit by a blizzard or heavy fog, they are literal life-savers because they'll always lead you somewhere, which, in the case of the Mystery Lake region, will be the lakeside hut or the dam. The same rule goes for power lines.
Now, speaking of the lake and fishing, here's a quick rundown:
You already know about the Camp Office and where's it located. It usually has some fishing lines inside (remember that they are tiny, and sometimes it's hard to spot them lying on the floor), and that's step one. Then just remember to grab an axe or crowbar, and off we go! The Camp Office is obviously located at the lake, so just find the nearest fishing hut. Make sure to wear warm clothes and choose a warm, sunny day, too, because this will take some time. Now, just enter the hut, use your tool to break the ice and start fishing. I've read opinions from seasoned Long Darkers that the fishing algorithm prefers longer sessions — pick three hours instead of one to get a better haul. Sooner or later, you'll get your first fish. If you're afraid of sudden temperature drops, bring some firewood, since the small fishing hut has its own stove.
If you want to get more advanced, you can cut some fishing bait from the fish you've already caught. This will increase the average weight of your haul. The workbench at the Camp Office lets you make lures, too, which give you a better chance to catch rare fish types. It's not necessary for survival but with the woodworking tools added in the late update, you can pick a piece of wood, stuff and frame your rare fish, and put it on the wall in your favourite hideout.
By the way, are you playing with the Scurvy mechanic turned on? Fish are a great source of Vitamin C, so learning basic fishing may get really helpful in the future. Also, if you're planning to play the Story Mode (Wintermute), one of the side quests involves catching a real monster worth 30 kilos of meat.
Anyways, so much prep talk. I'm really glad to see you post here. Keep us informed about your progress. Good hunting, Survivor!