‘Health’ is generally used to refer to things like pollution, etc. that cause long term chronic impacts.
Not individual sudden events which drown/murder massive numbers of people regardless of their general health status (except perhaps for their ability to run really fast and really far on no notice).
So are cholera and other diseases accompanying flooding.
And other factors associated with reservoirs: desertification and lake evaporation can lead to increased dust, common where water is diverted or impounded (Aral Sea, Lake Powell, Lake Mead). Disruption of silt flows has various impacts, more on the general environmental side.
Generally, if your concern is overall mortality risk rather than a specific disease/pollution mechanism, dams do not get a free pass.
The public health department doesn’t concern itself with things like national defense, if skyscrapers are likely to fall over or not, and local gang violence. Those have their own specialities.
Otherwise, literally everything is a ‘health issue’, including agriculture and commercial/residential zoning.
And notably, no one has actually provided any examples of where any of these are actually in major cities. Because it’s absurd, hah.
Not individual sudden events which drown/murder massive numbers of people regardless of their general health status (except perhaps for their ability to run really fast and really far on no notice).
Those are referred to as ‘disasters’.