"As I thought I understood it, then a new alien species would arrive and the whole thing would start again." David M. Harper, from the Department of Biology at the University of Leicester, is doing research at Lake Naivasha in Kenya for 30 years now. As an ecologist, he tried to understand the straight forward limnology of the lake. "And then I realised after about three or four years that the reason that the lake was functioning unpredictably was because it was full of alien species." What he learnt during this time reveals a lot what science is about. Simple explanations may be right for simple problems. But when it comes to ecological dynamics being influenced by humans and the other way around there is no such thing as simplicity. Therefore a more comprehensive approach is needed than a single discipline can offer. That is why Mr. Harper's work is an invaluable contribution to the understanding of the endogenous functioning of the system. But how to deal with external shocks, changes in governing institutions or the drastic increase in population? What are the consequences for the demand towards the lake? Can illegal water abstraction be prohibited by the existing institutions?