In cases of flooding many authorities and organizations become involved and it can be a problem to take in the whole situation and have a common picture when many incidents are happening at the same time. There is also a lack of efficient tools that show critical buildings and constructions in combination with actual and forecasted water levels. When handling critical situations people face challenges of complexity, uncertainty, and unpredictably. Such management and decision-making activities are normally supported by various models and support tools. However, complexity is normally not explicitly addressed in such models and tools. In this paper we analyze and discuss different kinds of complexity, which are a challenge in critical situations caused by flooding.