Virtually none of California's phosphate waste enters lakes and rivers, because that is our water source from the mountains. In most cases, the waste water enters a municipal treatment facility where microorganisms are killed, as much as possible, and phosphates filtered out. To my knowledge, no problems with too many phosphates or algae overgrowth in our oceans. The main seawater quality problem we have are streams that empty to the ocean that are NOT part of the water supply system. During the rainy season, these streams receive a lot of run-off water from storm drains, roof gutters, etc that goes into the ocean without treatment.
As a result, chemicals and microorganisms that would soak into the soil are instead carried out to the ocean (one reason our roof gutters drain to the street is to prevent erosion of our clay hillsides, which cannot absorb too much water or they "melt". Our city is building a system to capture this water, filter it, and use it for agricultural purposes (newer homes with TWO water meters, one for household and one for gardens; also the agricultural water can be used for farms, golf courses, etc.). Also, a lot of water seeps into the ground and the city operates three wells to utilize this naturally filtered water (for agricultural). The result is that the city has become a net EXPORTER of water during the November-May cool season, when there is little landscaping use of water; during these months, the city produces about 10,000,000 liters (2.5 million gallons) of EXCESS water DAILY, and exports it to cities without such a system (our city has a large seasonal creek that runs through it---other cities lack such a creek or stream).
However, there is a cost associated with this green activity: the fixed part of one's water bill (the part you pay even if you don't use a drop of water, to finance the operation of the system) is close to $40 per month. I have low water use landscaping plants, so my water use bill on top of the $40 is only $10-12, for a total monthly bill of about $50, but if I were away for a month on vacation in the winter with landscaping water turned off, I would still incur a monthly bill of $40. On the other hand, residents of nearby cities that import our water pay our city a fee, which must be reflected in higher water rates for them.
Northern Orange County, CA, has a huge seasonal river (Santa Ana River) that drains the large Southern California mountains (the local ski resorts), known as the San Bernardino Mountains (12,000 foot elevation). The river in central OC is full of honeycombed berms to PREVENT the water from reaching the ocean. The river is also protected by dykes, because there have been catastrophic floods in the past when there were no dykes. The idea is to capture the water, force it to percolate into the ground, and then it is pumped out by wells in central OC. Closer to the ocean, there are "injection wells" which force waste water INTO the ground, the reason is to prevent ocean salt water from migrating inland as water is pumped out by inland wells 10-20 miles (15-30 km) away from the ocean.
