The salinity difference between river- and sea-water gives rise to a free energy difference of 2kJ per liter river water, which corresponds to a waterfall of 200 meter. This “blue energy” can be harvested fully sustainably in principle, and nowadays also largely in practise with the use of ion-selective membranes or supercapacitors. Most experiments so far involve cold river- and sea water, but our calculations show that warm river water (heated by waste heat) of 50 degrees can double the amount of harvestable blue energy. Much more impressive, however, are recent experiments with river- and sea-water separated either by solid boron nitride (BN) membranes punctured with highly charged nanotubes or by a single-layer of molybdenum disulfide (MoS2) punctured with nanoholes. These systems exhibit ionic currents that correspond to a “blue power” output of the order of 10^3 to 10^6 W/m^2, to be compared to only 5 W/m^2 with conventional ion-selective membranes. These spectacular findings motivate us to theoretically model ionic transport through charged channels by means of (modified) Poisson-Nernst-Planck-Stokes theory, which revealed (as an intermediate result) an explanation of hitherto ill-understood experiments on the surprisingly large influence of fluid flow on surface chemistry. In the future, we will build on this theoretical framework to further analyse the observed blue-power densities and other iontronic devices, inspired by e.g. the electric eel that can self-generate a voltage of 600V and an electric current of 1A by means of a smart geometry combined with ionic pumps or by the human kidney that can extract urea from blood with an efficiency that exceeds the best artificial purification device by a factor of hundred.