Table 2. Spearman correlation matrix of the percent resistances to the eight drugs in seven of the nine sampling sites.

	AMP	C	LEV	TE	CN	SXT	SMM	CTC
AMP	1.000	–	–	–	–	–
C	0.898**	1.000	–	–	–	–
LEV	0.503	0.524	1.000	–	–	–
TE	0.048	0.286	0.286	1.000	–	–
CN	0.587	0.452	−0.048	0.333	1.000	–
SXT	0.934**	0.905**	0.548	0.214	0.595	1.000
SMM	0.311	0.405	0.000	0.071	0.262	0.524	1.000
CTC	0.036	0.286	0.143	0.952**	0.357	0.119	−0.071	1.000

The sites of Haizi reservoir and Cuo River upstream have been removed based on the low antibiotic levels and few E. coli isolates, respectively. AMP = ampicillin, C = chloromycetin, LEV = levofloxacin, TE = tetracycline, CN = gentamycin, SXT = sulfamethoxazole-trimethoprim, SMM = sulfamonomethoxine, CTC = chlortetracycline). ^** indicate the significance level of p<0.01.