Lymph contamination of peripheral blood samples is common in reptile species due to a close association of the lymphatic and vascular systems. Grossly lymph-diluted samples are generally discarded due to potential effects on hematologic and biochemical parameters. Differences in biochemistry values from different sample sites in chelonians are often attributed to lymph contamination. Previous studies have evaluated blood–lymph mixtures but provide limited information because the proportion of lymph is unknown. Differences in biochemistry values of pure lymph compared to plasma are unknown in chelonian species. Paired plasma samples collected from the jugular vein and lymph samples collected from the dorsal lymphatic ring adjacent to the subcarapacial plexus were collected from 11 (6 female, 5 male) Krefft's river turtles (Emydura macquarii krefftii) for comparison of biochemical analytes. No statistically significant differences were found between lymph and plasma samples for chloride, glucose, alanine aminotransferase, aspartate aminotransferase, creatine kinase, urea nitrogen, and total bilirubin. Statistically significant (P ≤ 0.05) differences were found between lymph and plasma samples for gamma-glutamyltransferase (GGT), total protein, globulin, and uric acid. Sex and sample differences were statistically significant for sodium, potassium, calcium, phosphorous, magnesium, lactate dehydrogenase (LDH), albumin, and triglycerides, while significant sex differences only were found for alkaline phosphatase, cholesterol, and iron. Severe lymph dilution (1:1 with plasma) may cause clinically significant decreases of potassium, total protein, globulin, and LDH, and increases of GGT and uric acid in both sexes, as well as clinically significant decreases of calcium and triglycerides in female Krefft's river turtles.