Yellow phosphorus is extremely toxic to aquatic life. In herring, salmon, and lobster, the toxic effect of phosphorus is irreversible and probably cumulative. For herringLT50(hours) = 300/C0.87, where C = μg/liter of phosphorus. No clear indications of an incipient lethal level were found, anLT50being obtained even at a concentration of 2.5 μg/liter. Incipient lethal levels of yellow phosphorus for lobster, salmon, and beach flea are 40 μg/liter, 18 μg/liter, and 3–4 mg/liter, respectively. Poisoned fish turn red and show signs of extensive hemolysis. Blood of lobster congeals, and after death the thorax may be filled with thick gel and the heart grossly distended. For lobster,LT50(hours) = 300–0.17x, wherex= product of phosphorus concentration and exposure time (μg days/liter). The oxidation of dispersions of yellow phosphorus in water is kinetically a first-order reaction with half-life of 2–7.5 hr. The adsorption of yellow phosphorus on a solid support such as bottom mud substantially decreases the rate of oxidation.