The monthly average of (a) upwelling and (b) river flow over 20 years showing the annual pattern for upwelling and river flow in the Salish Sea. The strongest upwelling occurs during the summer months, while river flow is strongest during late spring, early summer. Phytoplankton populations increase during the summer due to longer daylengths, allowing the phytoplankton to access the nutrients. Perhaps our nutrient data reflect increasing phytoplankton abundances. The phytoplankton could be removing the nutrients from the water, masking increases in nutrient input. Stronger river flow could also be flushing the nutrients out of the system.