Reconnaissance investigation of water quality

A construction game system having cube-shaped corner pieces and construction rods of equal cross section, which comprises construction rods and corner pieces including side faces, the side faces of the construction rods and of the corner pieces has parallel disposed, dovetail shaped grooves, the corner pieces and the construction rods define a hollow space of substantially square cross section between the end faces. Further construction elements are provided as connection, fortification, and holding-members, the members are equipped with one of the same grooves and projections. At least one connecting member has such cross section that it is at least partly insertable into the hollow spaces of the corner pieces and of the construction rods and are lockable by means of holding members.