The aim of this work was to develop a molecular tool to positively identify brown bullhead catfish using environmental DNA (eDNA) that is suspended within the water column. The project had five main objectives: 1) to develop a protocol for the collection of eDNA, 2) to select and test primer sets that are specific to brown bullhead catfish, 3) to optimise DNA extraction and amplification, 4) to validate the methodology through sequencing the amplified DNA, and 5) to evaluate its sensitivity by sampling at various sites that had a range of catfish abundances. Water was sampled from Lake Rotoiti from a boat with a 1 litre labelled plastic container attached to a telescopic pole, retrieving water samples about 30 cm above the lake bottom in about 2 m of water depth and from deeper water. Each container was deployed container-opening facing down, and on reaching the desired collection depth, the opening was rotated uppermost to allow the entry of water. The full container was then pulled back to the surface, a plastic screw cap firmly screwed onto the container, and then subsequently placed in a chilly bin on a 20-cm layer of crushed ice. The collection was recorded on a GPS instrument.