Impact on Marine Life

Zooplankton are trapped on desal filters

Desalination plants have potential impacts on marine life at both ends of the pipe, the intake of ocean water and the discharge of brine back into the ocean.

Water Intake: Impingement and Entrainment of Marine Life
According to the Pacific Institute’s report, Desalination, With a Grain of Salt, A California Perspective, “Impingement and entrainment of marine organisms are among the most significant environmental threats associated with seawater desalination.” Impingement refers to mortality of marine life on screens as ocean water is sucked into the pipe. Entrainment refers to the mortality of smaller organisms such as plankton, fish eggs and larvae that pass through the screens and die during the pre-treatment process.

The Pacific Institute notes that “only limited research on the impacts of desalination facilities on the marine environment has been done.” However, more research has been done on power plants that use ocean water for cooling. “An analysis of coastal and estuarine power plants in California suggests that impingement and entrainment associated with once-through cooling systems have significant environmental impacts: “… impingement and entrainment impacts equal the loss of biological productivity of thousands of acres of habitat” (York and Foster 2005).1 Those power plants can process a hundred times more ocean water than the planned desalination facility in Santa Cruz. The extent of damage to marine life from small facilities such as the one proposed in Santa Cruz is unknown.

There are measures to reduce the extent of impingement and entrainment. Drawing water from pipes buried under a sandy ocean floor is one way to reduce the mortality of marine life. However, the local offshore geology is not conducive to that option. There has been no decision as to the location of seawater intake for the plant, but an option that is under consideration is the use of an abandoned waste water pipe that extends 2000 feet offshore from Mitchell Cove. In order to minimize marine mortality the City is considering multiple intake ports on the intake pipe. That will reduce the velocity of the water sucked in at any particular intake port, thus reducing the amount of impingement of the larger marine life on the intake screens. Small mesh screens may reduce entrainment of smaller organisms. But billions of micro-organisms that are at the base of the food chain will pass through the screens and become entrained on the desal filters.

The environmental impact report for the plant will evaluate the impact of impingement and entrainment of marine life, although the lack of research on this topic will limit the extent to which any firm conclusions can be reached.


As water passes through the reverse osmosis filter membrane, leaving the salt behind, a brine is created that is roughly twice as salty as ocean water. High concentrations of salt in discharged water can poison marine life. Santa Cruz intends to dilute this brine with water from the sewage treatment plant before discharging it into the ocean.
There are other wastes that will be discharged that are of concern. The Pacific Institute reports,
“Chemicals used throughout the desalination process may also be discharged with the brine. The majority of these chemicals are applied during pretreatment to prevent membrane fouling (Amalfitano and Lam 2005). For example, chlorine and other biocides are applied continuously to prevent organisms from growing on the plant’s interior, and sodium bisulfite is then often added to eliminate the chlorine, which can damage membranes. Anti-scalants, such as polyacrylic or sulfuric acid, are also added to prevent salt deposits from forming on piping. Coagulants, such as ferric chloride and polymers, are added to the feedwater to bind particles together.”2

There are no mitigation measures in the EIR for the Integrated Water Plan that address the biocides, anti-scalants, and coagulants that are discharged in the brine waste in the normal operation of the plant.3

Marine biologist, Cécile Mioni, reports that toxins from algae blooms could also be concentrated in the brine:
Monterey Bay is plagued with Harmful Algae Bloom (sometimes toxic, refer to death of birds and sea lions related to domoic acid in the area last summer). These blooms occur every year in Spring/Summer (PseudoNitzschia bloom with domoic acid production) and in Fall (red tide with dinoflagellates such as Akashiwo that sometimes produce toxins). The brine will most likely contain these harmful algae and concentrate them near shore in one spot. When a cell is exposed to too much salt/hypertonic solution, it shrinks and dies and can break open. If the cells break open, the toxins are released in the environment and can be concentrated in shellfish and other filter-feeders. This would be detrimental to endangered species feeding on these filter feeders (e.g. sea otters). See “Impact on Desalination of Harmful Algae Blooms in Monterey Bay”, by Cecile Mioni

Carol Reeb, a fisheries geneticist with Stanford’s Hopkins Marine Station, is concerned about the cumulative impact of the brine discharge from the eight planned desalination facilities in Monterey Bay. “The Monterey Bay is a semi-enclosed system which means it is protected from large offshore currents which could flush away brine waste. Coupled with the ebb and flow of tides and eddy-like circulation, this could allow brine plumes to entrain and accumulate along our coastline over the course of years.”5 Reeb notes that “Monterey’s Marine Sanctuary is home to 9 fish and an abalone listed under the federal Endangered Species Act.”

Precautionary Principle
When considering the environmental impact of a project, it is tempting to want a definitive answer. “Is it going to be harmful, and if so how harmful?” It doesn’t feel very satisfying to get the answer, “Intake of ocean water is definitely harmful when done on a large scale, but it is not known how harmful small scale intake will be.”

Environmental impact reports are written with the presumption that impacts can be classified as “significant” or “not significant”, when in fact the impacts of human action on the environment ripple out into the environment in a way that is not fully knowable. Every environmental impact report should contain the preamble, “This is the best we can estimate with our limited knowledge.”

The humility of scientists who recognize the limits of their knowledge has led to the development of the Precautionary Principle, a modern version of the ancient commitment, Primum non nocere. “First, do no harm.” The European Commission Communication on the Precautionary Principle describes it:
“The precautionary principle applies where scientific evidence is insufficient, inconclusive or uncertain and preliminary scientific evaluation indicates that there are reasonable grounds for concern that the potentially dangerous effects on the environment, human, animal or plant health may be inconsistent with the high level of protection chosen by the EU”.6

Planning eight desalination plants on Monterey Bay in spite of the reasonable grounds for concern about marine impacts does not seem to us consistent with a precautionary approach to conserving the natural world.
1 Pacific Institute, Desalination, With a Grain of Salt p. 59
2 ibid p 61
3 Final EIR, Integrated Water Plan (2005)
4 email correspondence 7/13/10
5 public comment at Ca. Public Utilities Commission hearing, 6/2010

One Response to Impact on Marine Life

  1. jeff kahler says:

    I do not think desal. is in any way an appropriate source of water for the Montery Pennisula or for Santa Cruz. The answer in my humble opinion lies in redistribution of the water we as Californians already have developed. Realizing that over 75% of all of California’s water is sucked down by agricultue and huge amounts of that water wasted on subsidized crops in many cases using antiquated and wasteful irrigation techniques, is the first and most critical step in solving our water needs. There is plenty of water avaiable in fact more than necessary if we would only address the agricutural

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