Flooding is a natural occurrence and no drainage systems or flood protection measures can give an absolute protection from all flooding events. The impact of flooding on a community and the health and safety risks are significant. Globally flooding is one of the natural catastrophes that every year causes most victims and the greatest economical effects. In Sweden and other European countries death caused by flooding is relatively unusual, but the damages in tangible assets and the cost for the society are considerable. In case of flooding many authorities and organizations become involved and there is a problem to take in the whole situation and have a common picture when many incidents happen at the same time. There is also a lack of efficient tools showing critical buildings and constructions such as roads, railroads, water-purifying plant, etc, in combination with actual and forecasted water-levels. In this paper we discuss how the critical factors can be visualized in the CRISSI system. The complexity challenges according to the laws of complexity are also considered.