What does snow-blindness refer to?

Oil slick causes mass scale death of fishes due to

Electrostatic Precipitator $(ESP)$:
$I.$ Is an electrical device to remove particulate matter present in the exhaust of thermal power plant.
$II.$ More than $99\, \%$ particulate matter can be removed by this method.
$III.$ $ESP$ has electrode wires and a stage of collecting plates.
Which of the statements given above are correct?

$A$ lake with an inflow of domestic sewage rich in organic waste may result in:

What is the density of heavy metals?

Frequent occurrence of water blooms in a lake indicates