Chainsaws, six-pronged spears and a whole lot of patience at -14C: How daredevil fishermen risk their lives catching prized 100lb sturgeon under frozen lake Daring fishermen risked their lives driving over a frozen lake in a bid to catch these prized sturgeon that weigh up to 100lbs. The brave anglers are currently creeping over Lake Winnebago, in Wisconsin, United States, during the 16-day spearing season. They use a chainsaw to skillfully cut through the 18-inch thick ice, in such a way the sunlight illuminates the water below the hole. These brave fishermen risk life and limb driving over a frozen lake in a bid to catch prized sturgeon that can weigh up to 100lbs Whopper: Each fish can weigh up to 100lbs and be more than 40 years old. Fisherman may only catch specimens measuring more than 3ft long It then takes the strength of three men to push the cut-out chunk of ice under the surface and out of the way, in temperatures as low as -14C. The heavily regulated sport - which often proves fatal - sees just a limited number of licences issued each year. There is then a rush from the second weekend in February to catch the sturgeon before the pre-determined quota or 16 days are up. Each fish can weigh up to 100lbs, and be more than 40 years old. Fisherman may only catch fish measuring more than 3ft long. Photographer Ivo Berg, 24, travelled to the lake, near Appleton, Wisconsin, to document the hunting, with a group he met once he arrived. Hole lot of trouble: The fishermen use a special chainsaw to skillfully cut through the 18-inch thick ice Laborious: After the hole is cut, it takes the strength of three men to push the chunk of ice under the surface and out of the way He said: 'Sturgeon spearing is a unique sport that is only allowed on very few lakes in Wisconsin and Michigan. If you have a licence, you can put your hole wherever you want. Some spots might be better than others, but its a matter of belief and taste. The guys I was with simply chose a spot close to the harbour, so they did not have to drive too far out onto the lake. Driving on the ice can be a dangerous game, and every year people will break into it and die. The team mark and cut out a hole to strict regulation size, and then cover it with a shack to alert others to the hazard and improve visibility in the water. Setting up camp: A shack is pushed over the hole that has been cut into the ice to give the fishermen a base to work from Ready and waiting: The shack contains a decoy to attract the fish, spears, a heater, stools, beer, and, once people are inside, patience The shack contains a decoy, spears, a heater, stools, beer, and - once people are inside - 'patience'. Each spear is a long, wooden pole, with a detachable head that comes off when a sturgeon is hit. Line attached to the head is then used to play and catch the fish. Ivo, from Berlin, Germany, added: 'The decoy is put into the water in order to attract sturgeons and help guage the size of the fish. You then have to wait, and finally decide about the size of the sturgeon before spearing. Only a decoy is allowed for attracting the fish - no bait, light, or other attractors can be used. Sturgeons often pass very low, on the bottom of the lake. As the water is very cloudy this year, we could only see something in about 6ft or 7ft depth, while the lake was about 12ft deep at our position. Deadly: Each spear is a long pole, with a detachable six-pronged head that comes off when a sturgeon is hit. The line is then used to play and catch the fish Bait: The decoy used to entice the fish into the area where the fishermen have cut the hole The season always starts on the second weekend of February and lasts up to 16 days. It can end earlier, if a quota limited is hit. If 90 per cent of the quota are hit, the next day will be the last day of the season. Every registered spearer is only allowed to take one sturgeon, and can be fined if it measures less than 36 inches. Every fish caught must be registered at a fish registration office, including the one Ivo photographed, which weighed 62lbs. Ivo, who was on his fishing trip, said: 'When the spear hits the fish, the top part of the spear comes off and you can pull the fish up by pulling the line. As soon as it is up high enough, you use a huge hook to grab him and drag him out of the water. Usually people will take the fish home and eat it. VIDEO The annual sturgeon spearing is part of the cultural calendar