  We have used the Submillimetre Common-User Bolometer Array (SCUBA) detector
on the James Clerk Maxwell Telescope (JCMT) to measure bright sub-mm emission
associated with a recently discovered extensive (>100/h kpc) and highly
luminous, `blob' of Ly-alpha emission at z=3.09. The blob lies within a known
large overdensity of optical sources in the z=3.07-3.11 range, and is centered
on a locally overdense peak within this region. The best explanation for the
copious sub-mm emission is a dust obscured continuum source, which may produce
the ionizing flux for the Ly-alpha cloud. Cooling gas explanations are
plausible but excessively complicated, and the 450/850 micron ratio rules out a
significant fraction of the signal arising from the Sunyaev-Zel'dovich
increment. At least two additional ~10 mJy sub-mm detections in the SCUBA map,
with a surface density significantly higher than in blank field surveys,
suggests that they may be associated with the z=3.09 structure. A SCUBA
`photometry' observation of a second nearby Ly-alpha blob tentatively detects a
weaker sub-mm counterpart.

Astrophysics