Swarm, Blood Algae

An oily substance in the water surrounds this seething red mass of wormlike lumps of algae.

Blood Algae Swarm CR 8

XP 4,800
N Diminutive plant (swarm)
Init +3; Senses low-light vision; Perception +0


AC AC 21, touch 17, flat-footed 18 (+3 Dex, +4 natural, +4 size)
hp 97 (13d8+39)
Fort +11, Ref +7, Will +4
Defensive Abilities swarm traits; Immune weapon damage, plant traits


Speed swim 20 ft.
Melee swarm (3d6 plus distraction)
Space 10 ft.; Reach 0 ft.
Special Attacks algal bloom, cling (DC 18), distraction (DC 18)


Str 3, Dex 16, Con 16, Int —, Wis 11, Cha 5
Base Atk +9; CMB —; CMD
Skills Swim +11


Algal Bloom (Ex)

Once every 2d4 rounds as a standard action while underwater, a blood algae swarm can release a cloud of red pigment in a 10-foot radius centered on the swarm. In this area, the water turns blood red and becomes opaque, blocking vision as obscuring mist. The pigment persists for 3 rounds before dispersing. The pigment colors the skin and clothes of any creature within the area a blood-red color for 1d4 hours, at which time the pigment fades. Scrubbing for several minutes with strong alcohol also removes the pigment.

Cling (Ex)

If a creature leaves a blood algae swarm’s square, several of the squirming creatures continue to cling to the victim. A creature with blood algae clinging to it takes 2d6 points of damage at the end of its turn each round. The creature can remove the algae with a successful DC 18 Reflex save as a full-round action. Any amount of damage from an area effect destroys all clinging algae, and the clinging algae also drop off automatically if the victim leaves the water or moves more than 30 feet from the blood algae swarm. The save DC is Dexterity-based.


Environment temperate or warm rivers
Organization solitary or colony (2–6)
Treasure none

Blood algae evolved from a species of river algae in the Jalrune River and has since spread to other rivers in Taldor and Qadira by adhering to the hulls of sailing ships. Individual creatures in a blood algae swarm consist of cells within a fat, gelatinous, wormlike matrix 4 inches long. A swarm of blood algae is at least 10 feet wide and consists of hundreds or thousands of these wormlike organisms.

Blood algae colonies form in river bends and places where the water flows slowly or forms stagnant pools seasonally. Multiple swarms make up a blood algae colony, which can spread across an entire river and writhe along its banks. Individual swarms rarely travel far from their colony unless flushed away by a flood or drawn away by a large log or river vessel—although a blood algae swarm may drift downstream when food is scarce to find a more plentiful area of the river.

Blood algae swarms are diurnal, floating toward the water’s surface in sunny weather and sinking to the bottom at night. These creatures absorb some nutrients directly from the water, but to survive longer periods of time, they must feed on living creatures such as crustaceans, fish, or mammals. Blood algae attach themselves to their prey’s skin, inserting needlelike protrusions in the flesh, through which they can feed.

Blood algae reproduce both sexually and asexually— although a swarm usually uses the latter method only when recovering from losses caused by environmental dangers or predation. A swarm of blood algae consists of a roughly equal number of male and female individuals, but members of the same swarm don’t usually reproduce with one another. Instead, a swarm seeks out another swarm for a violent-looking mating ritual, which churns the water with blood-red pigment.

Because blood algae swarms can color the water red, there are many superstitious beliefs in Taldor about evil spirits that turn the water into blood to punish people.

Section 15: Copyright Notice

Pathfinder Adventure Path #130: City in the Lion’s Eye © 2018, Paizo Inc.; Authors: Mikko Kallio, with Eleanor Ferron, Mike Headley, Joe Kondrak, Kalervo Oikarinen, and Liz Smith.

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