I've talked to Claire about this before and I think that she only analyzed for fecal coliform and had a student grab a sample in a makeshift container - its likely that the sample isn't representative of the water.
The South Platte is sampled by the USGS National Assessment of Water Quality (NAWQA) program. Here's the link to the online data retrieval: http://waterdata.usgs.gov/co/nwis/qw
Here's the link to the South Platte NAWQA study: http://co.water.usgs.gov/nawqa/splt/html/spdata.html
- you can access reams of data there. The NAWQA contact person is Lori Sprague with the USGS in Denver. She may be able to point you to more recent data than 1995 since they've been sampling recently for another phase of the program. Unfortunately its likely to be awhile until the recent data are released due to the extensive review process the USGS has.
I did some streambed sediment sampling between 8th and Zuni as a pre-construction assessment for when they get around to doing the restoration on that reach. It was a few years back and I'll check on whether the data are public record and can be released if anyone's interested. We didn't do any water sampling as part of my study though.
Remember to keep your mouth closed while boating at Effluence Park!