Background for Teachers

What Killed Freddy the Fish? Cover-Freddie the Fish

As you discuss "What Killed Freddy the Fish?" be sure to:

  • Explain that when one fish is found dead it's not necessarily cause for alarm. Pollution and harmful algal blooms (HAB’s) rarely kill just one fish, but when a fish is found dead, biologists set to work looking for more to determine if there is a "fish kill." If they find one, their next task is to determine the cause.
  • Help your children understand that nonpoint source pollution is often associated with runoff. It is pollution that usually cannot be traced to one single point of origination, hence the name "nonpoint" source. Freddy's case, with the lime at a construction site, could be considered point-source if just one builder had neglected to put proper runoff protection in place.  However, if there was development in a general area by several different developers, it would be hard to “point” and any one of them so we would call it nonpoint source. Freddy’s story is may seem to contradict that, but it is based on a real case, which took investigators a lot of time to figure out; it was extremely difficult to determine the source of the pollution that actually killed the fish because of the issue of runoff.

  • The reason homebuilders add lime to the soil before building (to increase stability) gives you a great chance to review the concept of erosion with your students.
  • Explain that the water that drains into storm drains (also called "storm sewers" or sometimes just "sewers") leads directly to our streams and creeks, which, in turn, leads directly to our rivers. Anything that goes into a storm drain will affect the quality of the water and the life that lives in it.
  • "pH" is a bit too complicated to fully explain to 4th-graders so you probably won't want to delve too deeply into the specifics of why the change in pH killed Freddy and his friends. However, here's a very brief explanation: pH is how acid or base a liquid is.  Pure water is neutral.  Fish require a certain range of pH for their gills and bodies to work properly.  Sometimes they can endure a slow change within the range they can stand. In this case, the lime elevated the "pH" levels extremely rapidly, causing problems for the fish that extend beyond the scope of this discussion. The bottom line is that the "pH" changed far too quickly for the fishes' bodies to adjust (and, actually, far too much for them to ever have been able to adjust).

Dangerous for Fish

Natural Causes

Greg Southard, an Aquatic Animal Health Inspector for TPWD, says that in order to determine if a fish died of natural causes biologists will first attempt to age the fish. He explains, "Texas Parks and Wildlife Department biologists can age fish by counting the rings on a structure called an otolith within the inner ear of fish - much in the same way that trees are aged by the rings in the tree's trunk."

Otolith are created from calcium carbonate and gelatinous matrix. Since fish never stop growing, the otolith will continue adding rings. However, as a fish matures, its growth will slow down significantly and the rings on its otolith will grow closer together. Each ring does not necessarily count as a single year; it will depend on many factors including the species, the conditions in which the fish lives, how quickly/slowly it now grows, etc.


Nonpoint source pollution:

Pollution that can't be traced to just one person or place. It comes from many different sources.

Helping children understand the concept of "runoff" can be tough. Doing something hands-on might be best. Demonstrate water traveling from Point A to Point B while you add detergents or other liquids to it as it moves. (This would be a great time to play outside in the dirt.) When the water arrives at its destination (Point B), ask the children how different it is from when it left.

Point source pollution:

Pollution that can be traced to one person or place. You can "point" your finger at it.

Discuss the fact that some items, such as motor oil, can be both nonpoint source and point source pollution.

Indicator Species:

Indicator species are animals sensitive to water quality and therefore give us information about what's happening to the water. They're a species whose presence, absence, or well-being can tell a lot about the health of the water in a particular area.

Golden Orb Mussel

Quadrula aurea  (Golden Orb) Mussel is an indicator species.

Mussels and clams make good indicator species in Texas because they are considered "filter feeders." Hence, they are filtering the water naturally, capturing samples that help scientists determine what's in that water. Also, they tend to stay in one spot and that helps scientists determine the water quality in one area.

Check out this article, part of the “Texas Living Waters Project.” It

Sabine Lake

Sabine Lake

discusses how clams are helping to determine the health of Sabine Lake:

And to learn about how amphibians act as important indicator species in Texas by listening to this short episode of the radio show "Passport to Texas:"

What Can You Do?

Discuss the following list from the Student Resources Page with your kiddos, making sure that they understand why each item helps prevent pollution. Ask them if they can think of anything to add.

  • Don't litter
  • Don't use plastic bags if you have another choice
  • Pick up every single piece of plastic you find before it blows into the water
  • Move sprinklers so they're watering the lawn or dirt – no sidewalks and driveways
  • Never dump anything down storm drains
  • Sweep driveways, sidewalks instead of using a hose to wash them off
  • Properly dispose of pet poop-poop
  • Tell your friends, family, neighbors what you know about water pollution
  • Recycle soda cans, plastic bottles, and plastic bags

Harmful Alga Bloom (HAB)

According to Greg Southard, Aquatic Animal Health Inspector for TPWD, algal blooms cause problems for fish in two primary ways.

Says Southard, "One way that algal blooms can cause problems is by lowering dissolved oxygen levels in the water to concentrations not suitable for fish to respire properly. Algae can reproduce to large numbers or 'bloom,' but eventually the algal cell will die when conditions are no longer suitable for the bloom to occur. Other microorganisms such as bacteria will decompose all of these dead algal cells and through that decomposition process dissolved oxygen is decreased in the water, which can be harmful to other aquatic life such as fish. Another way that algal blooms can cause fish to die is by the production of toxic substances which can affect the gills and other important organs in fish that are needed for survival.

Golden alga is one type of HAB that's been particularly troublesome in Texas. Here's where you can find more information about golden alga:

This site has videos and photos about golden alga:

To learn about other HAB's in Texas visit:

Nonpoint Source Pollution

Nonpoint source pollution accounts for about two-thirds of all water pollution. Cindy Loeffler, TPWD water resources branch chief, explains: "Unique threats to urban streams and creeks include nonpoint source runoff from overuse of fertilizers and herbicides on landscapes and from impervious surfaces like parking lots and roads." Where rainfall cannot soak into the soil, it runs off, taking chemicals that have settled on the surface with it (i.e., oil from parked cars).

Impervious surfaces are surfaces into which water cannot soak so it’s forced to run off. In urban environments especially, many surfaces fit that bill. Roofs, concrete, asphalt and gutters – we seem to find them taking the place of dirt rather often these days.

The U.S. Geological Survey has a wonderful site that explains in detail how runoff works:

Examples of Nonpoint Source Pollution

As you discuss the examples of nonpoint source pollution with the children, always go back to the question, "How did that pollution get into the water?"

The goal is to make the connection between how our actions on land affect the animals that live in the water. It's very important that the children take from this unit an understanding that what we do in our yards, driveways, and playgrounds really does affect the fish in the water.

That's a pretty large leap for a 9 or 10 year-old to make, but with your great teaching they can do it!

Point Source Pollution

The distinction between point source and nonpoint source pollution is whether an entity can be held accountable.  It can be a little confusing when considering personal accountability. Think of it this way, you could identify the particular child whose papers scattered across the parking lot, or you could identify the elementary school with a trashy schoolyard that blows into the creek, or you could identify the community whose downstream neighbors accuse of trashing their fishing spots.  While there is definitely individual responsibility throughout, that would all be considered nonpoint source.  In contrast, if the landfill didn’t properly cover the trash so that it blew into the same waterway trashing the same fishing spots, that would be point source.  It is much more difficult for individuals to do something about point source pollution because they would have to convince the decision makers at an agency or corporation to make policy or process changes.  However, every one of us can help control nonpoint source pollution by simply attending to what we do and how we do it.

Children need to get the clear understanding that nonsource point pollution is often done by accident. In fact, when it comes to nonpoint source pollution, people often don’t even realize that their actions are contributing to the problem. Source pollution, on the other hand, is a form of pollution that can be consciously and immediately prevented.

It is the awareness and the personal decision to prevent nonpoint source pollution that is particularly appropriate and empowering for youth.

Examples of Point Source Pollution:

Of the source pollution examples cited on the Student Resource Page, the one the children will likely have the most difficult time understanding is "Illegal Dumping and Discharges" so we recommend spending some extra time covering it.

Everything we do as individuals, businesses and communities produces waste.  There are laws about how the waste is handled to protect our environment and quality of life.  When those laws are obeyed that is legal dumping and discharge.  When those laws are broken, either deliberately or accidentally, that is illegal dumping or discharge

The BP Oil Spill of 2010 presents plenty of fodder for a conversation on that topic. Read "The Pain of the Spill" ( and "The Forgotten Deep" ( before leading the conversation so you’ve got some great background knowledge.

Make sure your children understand the difference between "illegal" and "legal." For your more advanced children, the BP Oil Spill will present plenty of opportunities to discuss issues of responsibility and stewardship.

We Also Suggest:

To gain the thorough background knowledge that will help you fully understand the effects of pollution and harmful algal blooms on our water wildlife, we highly recommend viewing the Texas Parks and Wildlife Department documentary, "The State of Flowing Water."

Access this remarkable documentary at: The show is broken into eight segments, which makes it easy to view it at your leisure.