Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

affect the water quality and quantity in basin surface waters.
In many basins, agriculture is the major water user and the major source of water
pollution to surface waters. In 1990, nearly 95% of the water diverted from the San
Joaquin River was diverted for agriculture. Additionally, 1.5% of the water was diverted
for livestock (Carter and Resh 2005). The amount and extent of water withdrawals or
diversions for agriculture impact streams and their inhabitants via reduced water
flow/velocity and dissolved oxygen levels. For example, adequate water flow is required
for migrating salmon along freshwater, estuarine, and marine environments in order to
complete their life cycle. Low flow events may delay salmonid migration or lengthen
fish presence in a particular water body until favorable flow conditions permit fish
migration along the migratory corridor or into the open ocean.
Water diversions may also increase nutrient load, sediments (from bank erosion), and
temperature. Flow management and climate changes have decreased the delivery of
suspended particulate matter and fine sediment to the estuary. The conditions of the
habitat (shade, woody debris, overhanging vegetation) whereby salmonids are
constrained by low flows also may make them more or less vulnerable to predation,
elevated temperatures, crowding, and disease. Water flow effects on salmonids may
seriously impact adult migration and water quality conditions for spawning and rearing
salmonids. High temperature may also result from the loss of vegetation along streams
that used to shade the water and from new land uses (buildings and pavement) whereby
rainfall picks up heat before it runs off into the stream.
Currently, California has over 500 water bodies on its 303(d) list (Wu 2000). The 2006
list includes 779 stream segments, rivers, lakes, and estuaries and 12 pollutant categories
(CEPA 2007). Pollutants represented on the list include pesticides, metals, sediments,
nutrients or low dissolved oxygen, temperature, bacteria and pathogens, and trash or
debris. There are 2,237 water body/pollutant listings; a water body is listed separately for
each pollutant detected (CEPA 2007). The 2006 303(d) list identifies water bodies listed
due to the presence of specific pollutants, including carbofuran and elevated temperature
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