Dark brown, and relatively large (about 1/2" long). Found both on the underside of the same rubber dock float. Rolled up in a ball when picked up, pill-bug style, but unrolled relatively quickly. Looked like they came straight from a Miyazaki movie! Sketchy initial ID as per http://tolweb.org/notes/?note_id=4182 (does anyone want to look them up for me in the Light Manual?). However they are solid dark brown, not mottled, as other iNat obs of this species have been.
Infested with several smaller grey isopods visible in some of these photos (assuming parasitic from behavior); see separate observation for them.
Water quality: 2:20 pm
Temperature in 2-3" water 22 degC
Salinity 28 ppt
Dissolved oxygen 7 ppm
pH 7
Salinity 18 ppt/23 ppt
Water temperature 18 degC/18 degC
Secchi 125 cm, Depth 200cm
pH 7.5, Dissolved Oxygen 6 ppm/4 ppm