Blood Algae

Blood algae (Calanoida sativum) is a hazardous species of plankton that began to flourish in the scum of swamp ponds in Mort Myre and the Haunted Woods of Morytania late in the fifth age. It excretes a hazardous waste that can harm most creatures native to Morytania, ranging from tiny leeches to hulking demons.

Origin
Over the many years of the Myreque effort, a residue of garlic and silver built up in the swamps of Morytania, largely as a result of over-land transportation of supplies and constant skirmishes against vampyre kind with soft silver weaponry. Constant exposure to these substances, in tandem with the toxic slime of venomous swamp snails, enabled a new species of plankton to gradually mutate in the stalid swamp ponds. Because most predators native to Morytania were harmed by the excretions of this new kind of swamp scum, it was able to breed and flourish unhindered and eventually grew widespread in water sources dotted around the landscape. It wasn't until the substance reached this population level that it was discovered by vyrewatch performing routine sentry patrols through Mort Myre.

Traits
Blood algae has a number of traits that allow it to be identified from or blend in with other kinds of pond scum.

Identification

 * It emits an odor similar to garlic
 * Its excretions often include tiny, shimmering silver particles, most of which settle to the bottom of the water source it is growing in.
 * The fluid excretions of blood algae are swampy green, and cannot easily be confused with clean water.
 * The pond scum itself appears to be exactly like any other, growing on the surface of water sources like a carpet.

Harmfulness

 * Its excrements are physically harmful to races and creatures often described as "unholy," such as demons, vampyres, corrupt werewolves, etc. This is especially true for creatures that subsist off of the nutrients in the blood of other creatures.
 * To those creatures it harms, it behaves similarly to holy water, but the effects are amplified tenfold. Most, if not all, creatures who are resistant to holy water are not immune to this substance, including fully matured vampyres.
 * Exposure to the toxic excrements of blood algae causes chemical-like burns to skin, often accustomed by loud sizzling sounds and smoking at the point of contact. Ingesting this substance would cause a painful sensation similar to consuming very high-proof alcohol and later weakness, stomach pains, nausea, and similar symptoms of stomach illness.
 * A creature the size of a normal human would need to drink multiple litres of this fluid to be killed by ingesting it. However, it takes less fluid to incapacitate such a creature than it does to kill it.
 * Blood algae excrements are able to kill a large victim in high dosage, but is more effective as a tool for sedating or causing physical pain, since the volumes required to kill would be difficult or costly to administer.