One of my favorite hikes in North Iceland. It is not a very hard hike. It takes about 45 minutes to walk up to the lake.
You park your car at Háls (a white house with a blue roof) and behind the house the trail starts (with yellow poles). You have to walk through a gate and walk along the fence (the fence is on your left side).
You can just stop at the lake, but you can also walk around it (