Water hyacinth | Eichhornia crassipes

California Pest Rating for
Water hyacinth  |  Eichhornia crassipes
Pest Rating: None  |  Proposed Seed Rating: None


 Initiating Event:

This plant has been rated as “Q” on the CDFA Plant Pest Rating since 4/20/2015.

History & Status:

Water hyacinth is a perennial herbaceous aquatic plant native to South America. Water hyacinth is generally free-floating but in situations where the vegetation is dense enough, the leaves may become emergent. It has been found on the San Joaquin River and in the Sacramento-San Joaquin Delta as well as in many lakes, ponds and rivers throughout most of California except for the north and in the mountains. Water hyacinth can form thick mats across the water causing problems for boats, fish, and water infrastructure. It can spread rapidly through quick vegetative growth and (occasionally) through seed production. The floating plants easily disperse and can block waterways and bays or be redistributed in a few hours depending on wind currents. It is invasive as it can displace native flora, possibly resulting in habitat impacts on native fauna by reducing oxygen content in of bodies of water. Water hyacinth populations increase in size rapidly by vegetative reproduction and form dense mats. These mats can infest irrigation canals. Because of its attractive flowers, it is a popular pond and water feature plant. It is widely available in nurseries during the summer months.

Official Control:

An extensive control project is being carried out by the state of California of water hyacinth in the Delta.

California Distribution: Water hyacinth has been found throughout California in waterways from the Delta south. It can be found north of the Delta during warm weather, but these plants are generally killed by cold weather.

California Interceptions:  Specimens have been sent to CDFA for confirmation.

Consequences of Introduction:
  1. Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. The risk is Medium (2), as the plant can occur in many wetlands such as the Delta.

—Low (1) Not likely to establish in California; or likely to establish in very limited areas.

—Medium (2) may be able to establish in a larger but limited part of California.

—High (3) likely to establish a widespread distribution in California.

  1. Known Pest Host Range: Evaluate the host range of the pest. Risk is High (3) as weeds do not require any one host, but grow wherever ecological conditions are favorable.

—Low (1) has a very limited host range.

—Medium (2) has a moderate host range.

—High (3) has a wide host range.

  1. Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Risk is High (3). The plant produces well by spreading rapidly in water via vegetative growth. It may also form seeds that can germinate under the right conditions.

—Low (1) does not have high reproductive or dispersal potential.

—Medium (2) has either high reproductive or dispersal potential.

—High (3) has both high reproduction and dispersal potential.

  1. Economic Impact: Evaluate the likely economic impacts of the pest to California using the criteria below. Risk is High (3) as the plant can impede irrigation, boating, fishing, and swimming. It ruins views of water, threatens water supplies (blocks canals, pumps, dams), and increases flooding.

A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.

—Low (1) causes 0 or 1 of these impacts.

—Medium (2) causes 2 of these impacts.

—High (3) causes 3 or more of these impacts.

  1. Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.  

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes
B.  The pest could directly affect threatened or endangered species
C.  The pest could impact threatened or endangered species by disrupting critical habitats
D.  The pest could trigger additional official or private treatment programs
E.  Significantly impacting cultural practices, home/urban gardening or ornamental plantings.

Risk is High (3) as the plant invades the water systems of California, disrupts natural lake communities and potentially could lower biodiversity by covering lake surfaces.  It can block birds’ access to water. Dying plants steal oxygen in water. It can impede mosquito control.

—Low (1) causes none of the above to occur.

—Medium (2) causes one of the above to occur.

—High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Water hyacinth

Add up the total score and include it here. (14)

Low = 5-8 points

—Medium = 9-12 points

—High = 13-15 points

  1. Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. Score: -3

—Not established (0) Pest never detected in California, or known only from incursions.

—Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

—Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

—High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas. 

7.  The final score is the consequences of introduction score minus the post entry distribution and survey information score: (11)


Known invasive in California. Minimal uncertainty.

Conclusion and Rating Justification:

A terrible weed in California. Similarly invasive and widespread plants have been given a C rating. Nevertheless, such a regulation would harm agriculture by preventing the sale of a popular nursery plant. Any regulation of this plant would have little or no consequence in limiting its invasiveness or reducing the costs of its management. Therefore, given its economic and horticultural importance, no rating is recommended for water hyacinth at this time.


Baldwin, B. G., D. H. Goldman, D. J. Keil, R. Patterson, T. J. Rosatti, & D. H. Wilken, editors. 2012. The Jepson manual: vascular plants of California, second edition. University of California Press, Berkeley.

California Department of Boating and Waterways. Water hyacinth control Program. Accessed 4/20/2015: http://www.dbw.ca.gov/PressRoom/2014/140310WaterHyacinth.aspx

Consortium of California Herbaria. Accessed 4/20/2015: ucjeps.berkeley.edu/consortium/

Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  16+ vols.  New York and Oxford.

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 654-0312; plant.health[@]cdfa.ca.gov.

Comment Period:  CLOSED

The 45-day comment period opened on Tuesday,  May 26, 2015 and closed on July 10, 2015.

Pest Rating:  None |  Proposed Seed Rating: None

Posted by ls