Writing prompt Grade 8 Health & Consumer Science
The Tessaly Reservoir Fish Advisory: An Explanatory Prompt
Students write an explanatory article for anglers' families on how mercury builds up in fish at a fictional reservoir and how to use a meal advisory to eat fish safely.
Objectives
- Students will explain in writing how mercury moves from the air and watershed into the largest fish in a reservoir.
- Students will explain who is most at risk from methylmercury and why cooking or cleaning a fish does not remove it.
- Students will use a fish advisory table to describe how a family can keep eating fish safely.
Vocabulary
- Watershed
- A watershed is all the land where rain that falls will drain to the same stream, river, or lake. Everyone lives in a watershed, no matter how far from the water they live.
Also: mercury, methylmercury, plankton, biomagnification, advisory
Teacher overview
Fish are a healthy food, yet in many lakes and reservoirs some fish carry enough mercury that health departments publish advisories limiting how often people eat them. This prompt asks eighth graders to write an explanatory article for the family newsletter of an anglers' club at the fictional Tessaly Reservoir, explaining how mercury moves from the air into the largest fish and how families can use the advisory to keep eating fish safely. Teaching note: students often assume that a fish that looks healthy, caught in water that looks clean, is safe to eat, or that cleaning and cooking a fish removes the mercury. Methylmercury cannot be seen, it is stored in the muscle that people eat, and no cooking method removes it, which is why the advisory depends on the kind and size of fish and on who is eating it.
Prompt
Read the background, then write your article.
Background: mercury in the Tessaly Reservoir
The Tessaly Reservoir is a fictional lake where many families fish for bass, walleye, perch, and sunfish. The county health department has posted a fish advisory at the boat ramp. The advisory does not say the water is unsafe for swimming or boating. It is about eating fish.
Where the mercury comes from. Mercury is a metal. It enters the air when coal is burned and from some mining and factory work, and it also comes from natural sources such as volcanoes. Mercury in the air can travel long distances. Rain and snow carry it down onto the reservoir and onto the land around it. That land is the reservoir's watershed, the area where rain drains toward the water. Runoff from the watershed washes more mercury into the reservoir.
How it changes and builds up. In the mud at the bottom of the reservoir, bacteria change some of the mercury into a form called methylmercury. Living things take in methylmercury easily. Tiny floating organisms called plankton absorb it from the water. Small fish eat large amounts of plankton, and larger fish eat many small fish. At each step, methylmercury stays in the animal's body instead of passing out quickly. It becomes more concentrated as it moves up the food chain. This is called biomagnification. Large, older predator fish, such as walleye and big bass, carry the most.
Why it matters for health. Methylmercury can harm the brain and nervous system. The greatest risk is to unborn babies and young children, because their brains are still developing. Methylmercury is stored in the fish's muscle, the part people eat. Trimming off the skin and fat does not remove it, and neither does cooking.
Why fish still belong on the table. Fish provide protein and healthy fats. The advisory is meant to help families choose which fish to eat and how often, so they can keep eating fish.
The Tessaly Reservoir advisory (in our scenario)
| Fish | Size | Most adults | Children under 15 and people who are or may become pregnant |
|---|---|---|---|
| Sunfish and bluegill | Any size | Up to 2 meals a week | Up to 1 meal a week |
| Yellow perch | Any size | Up to 1 meal a week | Up to 1 meal a week |
| Largemouth bass | Under 14 inches | Up to 1 meal a week | Up to 1 meal a month |
| Largemouth bass | 14 inches or longer | Up to 1 meal a month | Do not eat |
| Walleye | Any size | Up to 1 meal a month | Do not eat |
Your task. Write an explanatory article of four to six paragraphs for the Tessaly Anglers Club family newsletter. Explain how mercury gets into the reservoir's fish, why some fish carry more than others, who is most at risk and why, and how a family can use the advisory to keep eating fish safely. Define at least three terms in your own words, such as watershed, methylmercury, and biomagnification. End with a conclusion that follows from your explanation.
Planning Organizer
Fill in every row before you draft. Each row becomes part of your article.
| Part of my article | My notes and the evidence I will use |
|---|---|
| Introduction: what the advisory is and why families should read it | |
| How mercury reaches the reservoir (sources and path) | |
| How mercury changes and builds up (use the key terms) | |
| Why big predator fish carry the most | |
| Who is most at risk, and why | |
| How to use the advisory (give one example from the table) | |
| Terms I will define, in my own words | |
| Conclusion |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response
Anyone who has launched a boat at the Tessaly Reservoir has seen the fish advisory posted by the ramp. The sign does not mean the reservoir is unsafe for swimming or boating, and it does not mean families should stop eating fish. It means that some fish in the reservoir carry mercury, and the advisory shows how to enjoy them without taking in too much.
Mercury is a metal that reaches the reservoir mostly through the air. It is released when coal is burned and from some mining and factory work, and it also comes from volcanoes. Once in the air, mercury can travel a long way before rain and snow bring it down. Some falls straight into the reservoir. The rest lands on the watershed, which is all the land around the reservoir where rain drains toward the water, and runoff carries it in.
In the mud at the bottom of the reservoir, bacteria change some of the mercury into methylmercury. Methylmercury is a form of mercury that living things absorb easily and do not get rid of quickly. Plankton, the tiny organisms floating in the water, take it in first. Small fish eat huge amounts of plankton, and bigger fish eat many small fish. Because the methylmercury stays in each animal's body, it becomes more concentrated at every step up the food chain. This buildup is called biomagnification. It explains why large, older predator fish like walleye and big bass carry the most mercury, while sunfish, which are small and eat lower on the food chain, carry less.
Methylmercury can harm the brain and nervous system, and the people most at risk are unborn babies and young children, whose brains are still developing. That is why the advisory has a separate column for children under 15 and for people who are or may become pregnant. Families should also know that cleaning and cooking do not help. Methylmercury is stored in the fish's muscle, which is the part people eat, so trimming the skin and fat or frying the fish does not remove it.
The advisory makes it possible to keep fish on the menu. For example, most adults can eat up to two meals of sunfish or bluegill a week, and children can eat up to one. A largemouth bass that is 14 inches or longer is different, because most adults should eat it no more than once a month and children should not eat it at all. A family that catches a big bass can release it and keep the smaller sunfish for dinner instead.
Fish give families protein and healthy fats, and the Tessaly Reservoir is a good place to catch them. Mercury in the fish cannot be seen, smelled, or cooked away, so the advisory is the best guide to safe meals. Choosing smaller fish that eat lower on the food chain, and following the stricter column for children and pregnant family members, lets everyone keep fishing and eating well.
Rubric
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Explanation of the process | The path of mercury is missing or incorrect. | The article names sources of mercury but skips how it changes or builds up. | The article explains the sources, the change to methylmercury, and biomagnification in the correct order. | The article explains the full path and uses it to explain why fish size and diet predict mercury level. |
| Evidence and details | Few details from the background are used. | Details are included but some are inaccurate or unexplained. | Accurate details support each part, including who is most at risk and one example from the advisory table. | Details are accurate and well chosen, and the article compares two advisory entries to show how size and species change the limit. |
| Precise vocabulary | Key terms are missing. | Terms are used but not defined, or defined incorrectly. | At least three terms are defined correctly in the student's own words. | Terms are defined correctly and used again accurately later in the article. |
| Organization and conventions | Ideas are out of order, and errors interfere with meaning. | Paragraphs exist but transitions are weak, and errors are noticeable. | Four to six organized paragraphs with an introduction, clear transitions, a conclusion, and few errors. | Purposeful organization that moves from cause to health risk to action, with a conclusion that follows from it and nearly error-free writing. |
Differentiation
Support
Provide a partly completed flow chart of the mercury path (air, rain, watershed runoff, bottom mud, plankton, small fish, large fish) for students to label before they write. Allow these students to write four paragraphs and to define two terms instead of three.
Extension
Ask students to add a paragraph comparing a fish advisory with a swimming advisory after heavy rain, explaining why one is about eating and the other is about water contact. Students can also draft a one-sentence version of the advisory for the boat ramp that a younger child could understand.
ELL supports
Pre-teach "mercury," "plankton," "predator," "concentrated," and "advisory" with a food-chain picture that shows the fish getting larger at each step. Provide sentence frames: "Mercury gets into the reservoir when ___." and "Big fish carry more mercury because ___."
Extensions
Students can search their state health or environmental agency's website for a real fish consumption advisory and compare its format with the Tessaly table. A state fisheries biologist or a county environmental health specialist can be invited to explain how fish are sampled and how the meal limits are set.