Water-borne toxoplasmosis is increasingly recognised as a problem world-wide, and studies in California suggest that infectious oocysts reach the sea in freshwater run-off contaminated by cat faeces1. Novel Toxoplasma genotypes arise by recombination in the cat host2, and oocysts can be concentrated in filter-feeding invertebrates1. We have established that an atypical type II genotype causes fatal disseminated toxoplasmosis in Hector’s dolphins3 and in several native bird species in New Zealand4. We are currently conducting studies to characterise the distribution of this genotype in cat populations throughout New Zealand, and to assess levels of oocyst contamination in the coastal marine environment using mollusc species as bioindicators. Faecal samples collected from wild-trapped feral cats were examined by faecal float and by direct DNA extraction from faeces, followed by PCR targeting the Toxoplasma-specific dhps gene. Presence of T. gondii was confirmed by sequencing. Haemolymph was collected from commercially sourced and environmentally sourced greenlip mussels, and subjected to DNA extraction followed by Toxoplasma-specific PCR and sequencing. New Zealand appears to have an unusually high prevalence of infection in coastal mussels, with 12/56 (21%) commercially sourced mussels and 31/154 (20%) wild mussels testing positive on PCR. 4/133 (3%) feral cats were oocyst-positive on faecal float, and 40/97 (41%) whole-faeces DNA extractions processed to date were positive. We hypothesise that the higher prevalence on whole-faeces preparations reflects the presence of sexual phases of T. gondii within sloughed intestinal epithelial cells. Genotype analysis of 5 genetic markers revealed a possible atypical type #13 from two cat oocyst samples. Further genotyping is in progress for the remaining cat oocysts and the mussel samples. An extended study is underway on mussels at key coastal sites to detect changes in seasonal prevalence which may accompany factors such as increased surface-water input due to seasonal rainfall and snow thaw.