The "Cock lake" is not a lake at all, but a large stream
formed by water flowing out of the sands of Sandymount Strand
into a gully, after the ebbing tide has exposed the flats.
Stephen sees water flowing back in from this rivulet as the
tide rises: "In long lassoes from the Cock lake the water
flowed full, covering greengoldenly lagoons of sand, rising,
flowing. My ashplant will float away."
The photograph at right is posted on Dara Connolly's blog,
which contains images from a walk he took on Sandymount
Strand. He writes: "One thing I learned in recent weeks is
that the sand is not at its driest at the time when the tide
is lowest. The recently exposed sand flats hold a lot of
standing water in ripples and pools, and it drains off into
channels which resemble streams or rivers crossing the beach.
The largest of the channels is called 'Cockle Lake' on the
charts, or as Joyce would have it 'Cock Lake'. The sand
continues to dry out for several more hours until eventually
inundated by the returning tide."
Cock Lake was not Joyce's invention. That name can be seen on
some contemporary maps, including the one at right. But
Connolly may nevertheless be right that "Joyce would have it"
this way, since Stephen urinates
in this paragraph, his urine mingling with the swirling waters
of the rivulet.