Directly from the Roundup MSDS

12. ECOLOGICAL INFORMATION
ENVIRONMENTAL DATA: Do not apply directly to water. Do not contaminate water when disposing of equipment washwaters.
ECOTOXICOLOGICAL INFORMATION: Studies performed with a concentrated solution of the isopropylamine salt of glyphosate indicate the following:
MON 0139 Technical (62%)
48-hr LC50 Daphnia: 930 mg/L, Practically Nontoxic
96-hr LC50 Bluegill: >1,000 mg/L, Practically Nontoxic
96-hr LC50 Trout: >1,000 mg/L, Practically Nontoxic
96-hr LC50 Carp: >10,000 ppm, Practically Nontoxic

Maybe it's not so bad. I looked at the Rodeo data and it basically said the same thing.