Depending on the source you look at, “eutrophication” refers to the process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates (Art, 1993).  Typically, when a water body undergoes eutrophication, it promotes excessive algae growth.

A cyanobacteria (algae) bloom in Province Lake, 2012.

The eutrophication of a water body can occur through natural and/or artificial nutrient sources.  Natural sources include stormwater runoff, atmospheric deposition, and/or the export of nutrients from wetlands.  Artificial sources include fertilizers, septic tanks, and/or industrial processes.

Stream bank erosion.  The deposition of sediments into water bodies increases the concentration of nutrients in the water body.

Lakes undergo natural aging that move them from nutrient poor (oligotrophic) to nutrient rich (eutrophic) over the course of several centuries depending on the area.  This process can take as little as a decade or two if lakes are put under additional stresses from urban runoff and population growth.  Eutrophic water bodies tend to hold less value and are less used for recreation that pristine, oligotrophic lakes.

Riparian Zone

The riparian zone is the interface between the land and a stream or river.  Riparian zones are EXTREMELY important landscapes acting as buffers or “biofilters” that protect aquatic environments from excessive sedimentation, polluted surface runoff, and erosion.  Riparian buffers are a natural feature on many landscapes, but in urban areas, many riparian zones are engineered to protect against the same potential pollutants and erosion.

The image above illustrates the riparian zone.  It parallels rivers and streams, usually well vegetated in natural systems.  This vegetation helps stabilize slopes, filter runoff, and provides habitat for many animals. (photo courtesy Benton County, Oregon)

Riparian zones also dissipate stream energy through meandering and vegetation.  This is a crucial function that helps limit erosion and flood plain damage during high intensity storms.

Heavily vegetated riparian buffer. (photo courtesy of NRCS)

Dissolved Oxygen

Dissolved oxygen (DO) is a water quality parameter that can give insight into the health of a lake, river, or the ocean.  Dissolved oxygen is a measure of gaseous oxygen dissolved in an aqueous solution.  Oxygen can get into solution via a few mechanisms, including diffusion from the surrounding area, aeration or turbulence (e.g. wind mixing, inlet streams, waterfalls, etc.), and as a waste product of photosynthesis.

Dissolved oxygen is important because without enough DO in lake bottom waters, fish kills can occur and nutrients that cause water quality degradation can be released into the water column.  The concentration of DO in a waterbody is highly dependent on the location, stratification, season, and morphology.  Below is a chart that lists concentrations and the influence on fish populations.



A TRIBUTARY is a freshwater stream that feeds into a larger stream, river, or other body of water.  The larger body of water that a tributary flows into is called the mainstem.  Tributaries do not flow directly into the ocean.

The map above shows the Salmon Falls River watershed and the many tributaries that  flow into it.  The Salmon Falls River is a tributary of the Piscataqua River which flows into the Gulf of Maine.

Tributaries carry runoff and seasonal meltwater to larger rivers.  These tributaries can also be called headwaters.  The point where a tributary meets a larger river is called the confluence.

An aerial view of the Amazon River Basin and its tributaries.


An ESTUARY is a partially enclosed, coastal body of water where a river meets the ocean.    Estuaries are transition zones between fresh river environments and saline ocean environments.  Estuaries are subject to the tides, waves, and changes in salinity based on precipitation and river flow.

The Great Bay Estuary forms at the end of the Piscataqua River and the Gulf of Maine.

Estuaries are also rich and important habitats for many species of marine life and support high productivity.  Estuaries are fragile ecosystems as they are influenced by both what happens upstream in the river and what happens in the coastal environment.

The mouth of an estuary.

Point and Non-point Source Pollution

Point Source and Nonpoint Source Pollution are the two broad categories of pollution in watersheds.  Lets start with point source pollution.

Point Source Pollution can be identified as pollution from a specific spot.  A drain pipe leading out of a building and discharging waste into a waterbody is an example of point source pollution.
Point source pollution was realized as a major problem in the late 1960s when the Cuyahoga River in Ohio caught fire from being so polluted.  This prompted the passing of the Clean Water Act in 1972 and the regulation of point source pollution.

The EPA term “point source” means any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged. This term does not include agricultural storm water discharges and return flows from irrigated agriculture.

Non-point Source (NPS) Pollution is pollution that cannot be tied to a specific pipe or drain.  NPS pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, and/or seepage.  Stormwater running off the landscape carries with it soils, nutrients, petrol, trash, pet waste, etc. and is deposited into a waterbody causing water quality degradation.

(photos courtesy of US National Oceanic and Atmospheric Administration (NOAA))


The word “watershed” is used all the time in water related discussions or settings.  We are all guilty of using words that come with our own line of work and not explaining them, so in this section we will aim to define and explain some words related to our field!

This week’s word is “WATERSHED”.  A watershed is an area or region of land that is divided by ridges or high points that drains to a body of water.  There can be watersheds inside of watersheds inside of watersheds as an area may be drained by stream (1 watershed), that meets a river (another watershed) that drains to a lake (yet another watershed) that eventually drains to the ocean (the largest of our watersheds).

This image depicts just such a scenario.  The dotted yellow lines show the border of different watersheds.  Although some small watersheds exist, all the water seen here drains to the large body of water at the base of the picture (either a large lake or ocean).

This image shows you the AWWA watersheds.  We work in all these watersheds to prevent erosion and stop polluted runoff from entering these lakes.



A reservoir can be a pond, lake or basin, either natural or artificial, for the storage, regulation and control of water.  Reservoirs can also include aquifers where groundwater is stored.

At AWWA we look to create reservoirs when we install our Best Management Practices (BMPs).  By doing this, we can allow more stormwater to infiltrate into the ground and be cleaned of nutrients and pollution before it enters a lake or stream.

Image Courtesy of the USGS