Úlfljótsvatn is a spring fed lake, as it is a drainage of Lake Þingvallavatn. There is a considerable current in the water where the average flow is 90 thousand liters per second. The lake is about 4 km² in size, is 80 m above sea level and is just over 20 m where it is deepest. Most of the catch is arctic char, but also some brown trout. The most common size of the fish is half to two pounds, but the number of larger fish has increased in recent years. The best time is from mid-June to mid-August.