Is it possibly:
Complexion?
A harbour once fashionable,
Coloured by dead lovers,
Alexandria. Center of the Hellenistic period, a period considered decadent.
The famous lovers Cleopatra and Mark Antony died here.
Coloured by - pigment
Loved by the young that later exude oriental smoothness,
Loved by the young - Good skin
Exude oriental smoothness - The young enjoy smooth skin, and Alexandria "later became a major staging point on the northern Silk Route."
And reportedly circled by the young that later either wash their faces,
Complexion?
Or occasionally observe mammalian explosion.
Pigmentation?
Harbour circled by:
Complexion + Alexandria + Pigmentation =
-------------- Original Answer ------------------
Maybe
Prince William Sound?
A harbour once fashionable,
Before Exxon Valdez
Coloured by dead lovers,
From wiki: "massive damage to the environment, including the killing of around 250,000 seabirds, nearly 3,000 sea otters, 300 harbour seals, 250 bald eagles and up to 22 killer whales"
Loved by the young that later exude oriental smoothness,
Exxon Valdez was previously known as Oriental Nicety, with smoothness referring to an oil 'slick'
And reportedly circled by the young that later either wash their faces,
Reference to the birds who were destroyed (covered by oil) when they bathed, washed, fished, etc.
Or occasionally observe mammalian explosion.
Reference to the whales and their behavior, with explosion also possibly referencing their demise.