Negotiating the Mesna trails during winter is a very different proposition during winter. You are better off abandoning the summer map and get your skis out. Above the rim where the terrain levels out, there is very good skiing on groomed and non-groomed trails through the vicinity of the river (and elsewhere). Get a ski map from the tourist office or the DNT office in town, or read the posters at most trail crossings.
Straight through Lillehammer runs the Mesna River. Not much to speak of, as the river bed in town centre seems full of trash and with little water. Hyd-el production has taken most of the water into a tunnel and through turbines underneath town.
However, if you continue up past the old power plant just east of MesnaSenter and the Old Car Museum, you will soon come to a nice area of forests, small cliffs, pools and waterfalls. Walking the trails here can be a nice and rewarding experience. Good picnic spots, too, and swimming is possible in the deeper pools. Watch for broken glass when bathing! Upriver you pass a strange house (northern bank) that used to be the home of the seer Marcello Haugen, and further, up at the plateau, you will arrive to the Mesna River canal where the hyd-el plant sucks in its water. From the upstream end of this canal there is a possibility of rening a canoe in order to continue further upriver in much calmer water than nearer town. Contact the tourist office for current facilities and information.
Just east of town, near the ski stadium lies the "undeveloped" Abbortjernet Lake ("Perch Lake"). No facilities here, but who needs that? You can walk or bike up from town past the ski jump area above town or use a car/taxi/bus to get to or close to the ski stadium and walk from here by help of a map and directions given by the tourist office.
The lake gets nice and warm during the summer season - much, much better , warmer and cleaner, than Lake Mjosa and the Laagen River, and is a favourite among the more sporty locals. Bring some food - the water you can drink as it is. Bring a tent, and you can stay overnight, too.
The river Laagen runs into Lake Mjosa at Lillehammer and forms a delta area which is quite nice. It is the richest freshwater fisheries area in Norway, but few people come here apart from locals. The delta consists of a few islands, shallows, sandbanks, bays and some deeper channels. The surrounding landscape is forested or agricultural land. You can get to the delta by foot from town, or by bike or car to get to other areas. It doesn't look particularily exciting, but grayling and whitefish here is abundant and easy to catch, likewise perch, pike, various carp fishes and giant brown trout. A smallish herring-type fish (lagesild) of the salmonide family spawn here during autumn (1st week of October - see separate tip) and gives rise to a spectacular fishery and abundant bird life. Apart from aquatic life, there are many birds and a variety of plants here, some common mammals including the beaver. Some of the plants are at their global northern range here. Waterfowl nest here and several Arctic species use the area as a resting place during spring and autumn migration.
To get around, the best idea is to use a rowing boat, canoe or kayak, or a bike if you are land-bound. The current is strong in the upper parts. You can go exploring, fishing, birding, watching plants, swimming. The latter is for the haried, though, as with warm summer weather the northern glaciers melt and feed the river, green, icy cold glacier water.
The Laagen River Delta is a protected nature conservation area, and includes some of the nearby cultivated fields and riparian brush, and no hunting or excessive collecting of plants is permitted.