Negro and Danube are mirror rivers
  We study the European river Danube and the South American river Negro daily water levels. We present a fit for the Negro daily water level period and standard deviation. Unexpectedly, we discover that the river Negro and Danube are mirror rivers in the sense that the daily water levels fluctuations histograms are close to the BHP and reversed BHP, respectively. 
R. Gon\c{c}alves, A. A. Pinto