Found in the Russian River from April - June. They're usually found at the edges of the river in fairly slow water. They range in size from 6-10 mm not counting cerci or antennae.
Yeah, the ones with the white spots show up at about the rate of about one out of twenty nymphs. Not sure why they show up, doesn't appear to be a sexual or territorial characteristic. Just a color variation? The white spots show up in the same areas on the nymphs that have them.
Based on this snippet from the scientific paper by M. D. MEYER AND W. P. MCCAFFERTY, Nixe kennedyi has been identified in the Russian River.
"Nixe kennedyi (McDunnough) Previous data.—McDunnough (1924): NAPA (Calistoga); Mayo (1952b): AMADOR (Amador Cr, Dry Cr); Day (1956): ALAMEDA. New data.—AMADOR: Niles Cyn, 8-V-1949, Day, A (CAS); BUTTE: Anderson Fork, N Chico, Rock Cr Rd, 11-V-1968, Evans, A (PERC), and Chico Cr, 13-V-1953, Abraham & Dart, A (CAS); FRESNO: Dry Cr, 14-V-1954, Ell, A (CAS); NAPA: Capell Cr, 7-VI-1952, Day, A (PERC); SISKIYOU: South Fork Sacramento R, 15-VII-1985, Courtney, A (PERC); SONOMA: Russian R, 2 mi N Cloverdale, 8-VII-1975, Rude, A (UCB); STANISLAUS: Stanislaus PG&E Power Plant Site, 5 mi N Turlock L, 15-IX-1976, Collins, A (UCB); TEHAMA: Salt Cr, 15-V-1954, Chandler, A (CAS)."
To my knowledge, of the (10) Nixe species found in North America (north of Mexico),Nixe kennedyi is the only species found in California. Do you believe the these nymphs to be Nixe kennedyi?
I don't know if these nymphs are Nixe kennedyi or not. Chances are pretty good that they are but the nymphs haven't been described yet as far as I know. The latest paper on the nymphs I can find is this one and it states in the Introduction that there is not a description of the nymphs of Nixe kennedyi.