Well...on one hand this one being inserted in "Impeding Doom" is exaggerated to a certain extent but on the other justified by Flandre's about to be using her power in a ... about to-be prank-ish trouble-ish manner... "Impeding Doom(light version)"...
P.S.It would be fitter for a new pool,if it is properly started and stocked,along the lines of "Watch out! Incoming!"even if they are unaware or little aware about.