[3] The membrane is two cells thick, soft and translucent, and grows attached, without a stipe, to rocks or other algae by a small disc-shaped holdfast.

[4][8] Ulva lactuca is very common on rocks and on other algae in the littoral and sublittoral on shores all around the British Isles,[9] the coast of France,[10] the Low Countries[10] and up to Denmark.

In August 2009, unprecedented levels of the algae washed up on the beaches of Brittany, France,[16][17] causing a major public health scare as it decomposed.

[16] In an earlier separate incident at the same beach in July 2009, a truck driver had died near his vehicle after hauling three truckloads of sea lettuce without protective gear during the annual cleanup.

Although initially recorded as a heart attack, the death of the truck driver prompted French authorities to exhume his remains for an autopsy.

[14][18] Environmentalists claimed that dead animals found on the algae-clogged beaches (including 31 wild boars in July 2011) were a result of toxic fumes.