Abstract: A method of isolating microorganisms and viruses, including phages, bacteriophages and cyanophages from an environment, particularly an aquatic environment, and propagating the isolated microorganisms or viruses for inoculum formulation. A specific target organism or selective growth medium is first immobilized in a stable substrate form such as sodium alginate gel pellets. The substrate containing the target organism or growth medium is then introduced into the environment to be sampled and microorganisms and/or viruses which are pathogenic to the immobilized target organism, or which can utilize the nutrient included in the growth medium, colonize the pellets. The colonizing microorganism or viral pathogens are removed from the gel pellets using standard laboratory techniques. One of the isolated pathogens, particularly an isolated viral pathogen, may be selected and propagated for inoculum formulation.