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Lesson plan Grade 12 Health & Consumer Science

Lake Callowmere Algal Bloom: Advisories for Four Kinds of Lake Users

A grade 12 health lesson where students read lake bloom toxin data, explain the nutrient link, and write advisories for swimmers, dog owners, anglers, and lakeside homes.

Objectives

  1. Students will explain how excess nitrogen and phosphorus, warm weather, and calm water combine to produce a cyanobacteria bloom.
  2. Students will use monitoring data to assign an advisory tier to each lake site and explain why visible scum is an unreliable guide to safety.
  3. Students will write a clear advisory that tells one group of lake users how the toxin could reach them and what to do.

Vocabulary

Key words: cyanobacteria, harmful algal bloom, microcystin, nutrient loading, phosphorus, advisory tier, exposure route

Teacher overview

Lake Callowmere, a fictional lake used for this lesson, turned green in late summer after a wet spring washed fertilizer, manure, and septic seepage into its tributaries, followed by weeks of hot, calm weather. The bloom is made of cyanobacteria, some of which produce microcystin, a toxin that can injure the liver and cause rashes, vomiting, and diarrhea in people, and that can kill dogs that swim in the water, drink it, or lick scum from their fur. Students read the county's fictional monitoring data, assign advisory tiers by site and week, and then write a short advisory for one group of lake users. The lesson connects a nutrient pollution problem to the specific health behaviors that bloom advisories ask of the public.

The misconception to address directly is that boiling makes lake water safe. Boiling kills bacteria and parasites, yet it does not destroy microcystin, and because it drives off water while the toxin stays behind, it can leave the toxin more concentrated. A second misconception, that clear-looking water is safe, is tested against the data, where one site's toxin level stays high after the visible scum has blown away. Seniors who take summer jobs at camps, marinas, or pet-care businesses may be asked about a posted advisory, so the writing task is framed as practice for that conversation.

Procedure

Hook (5 min): Read aloud a fictional voicemail left for the county health department: "Our dog swam at the east end of Callowmere this morning and now she is throwing up. My kids want to go to the beach this afternoon. And our cabin pumps its water straight from the lake. Can we just boil it?" Ask students which of the caller's three questions is most urgent and why. Record their reasoning.

Direct instruction (12 min): Explain the chain from nutrients to bloom. Nitrogen and phosphorus from lawn and farm fertilizer, manure, and failing septic systems feed cyanobacteria, and warm, sunny, still weather lets them multiply near the surface. Wind can push the floating bloom toward one shore. Some cyanobacteria release toxins, and the toxin dissolves in the water, so it can remain after the green scum is gone. Name the exposure routes: swallowing water, skin contact, and breathing in spray from activities such as water skiing. Explain why dogs face special danger: they drink freely, they swallow scum when they lick their fur, and they are small, so a given amount of toxin is a larger dose for their bodies. Finish by stating the rule for homes that draw water from the lake during an advisory: do not drink it and do not boil it, because boiling does not destroy the toxin and can concentrate it. Use bottled water or another safe source for drinking, cooking, infant formula, and pets.

Data analysis in pairs (13 min): Pairs complete handout items 1 through 7 using the fictional tier plan and monitoring table. Circulate and listen for students who assign tiers from the scum column instead of the toxin readings; ask them what the East Shore numbers show in Week 4.

Advisory drafting in groups (15 min): Divide the class into four groups, or eight in a large class, and assign each group one audience: families with young children at the Linden Cove swim beach; dog owners; anglers and boaters launching at Mill Inlet; and lakeside households at East Shore that draw water from the lake. Each group writes an advisory of about 150 words on chart paper for the Week 4 conditions. It must name the tier and where it applies, explain how the toxin could reach this audience, give three specific actions, say when to seek medical or veterinary care, and state what would need to happen before the advisory is lifted.

Gallery review and exit ticket (15 min): Groups rotate to two other posters and leave one sticky note each: one accurate statement they would keep, and one statement that is unclear or incorrect. Then students complete handout item 8 on their own as the exit ticket. Collect and sort the responses; if more than a few students still say boiling helps, open the next class with a two-minute demonstration or explanation of how boiling concentrates dissolved substances.

Lake Callowmere Algal Bloom: Advisories for Four Kinds of Lake Users — Grade 12 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Handout

Background. In our scenario, the fictional county health department samples three sites on Lake Callowmere each week and sends the water to a lab that measures microcystin, a toxin made by some cyanobacteria. Microcystin can harm the liver and cause rashes, vomiting, and diarrhea. Dogs are at special risk because they drink lake water, swallow scum when they lick their fur, and have small bodies. Boiling does not destroy microcystin, and because boiling drives off water, it can leave the toxin more concentrated. The toxin is dissolved in the water, so it can remain after the green scum is gone.

The county's fictional three-tier advisory plan (microcystin in micrograms per liter):

  • Caution, 4 to less than 10: Avoid swallowing water and avoid scum. Keep pets out of the water. Rinse off after swimming.
  • Warning, 10 to less than 20: No swimming or wading. Keep pets away from the water and shore. Lake water must not be used for drinking or cooking.
  • Danger, 20 or more: Stay out of the water and away from scum on shore. No water contact of any kind. Lake water should not be used for any household purpose except flushing toilets.

Sites. Linden Cove is the public swim beach. Mill Inlet is the boat launch, where a stream draining farm fields enters the lake. East Shore is a row of cabins that pump water from the lake for household use.

Fictional monitoring results (microcystin, micrograms per liter):

Week Weather notes Linden Cove Mill Inlet East Shore Scum seen at
1 Hot and calm 2 6 1 None
2 Hot and calm 5 14 3 Mill Inlet
3 Hot; strong west wind the day before sampling 8 22 12 East Shore
4 Cooler and calm 11 18 12 None
  1. Which advisory tier applied at Mill Inlet in Week 3?
  2. In which week did the Linden Cove swim beach first reach the Warning tier?
  3. Which site was the first to reach any advisory tier?
  4. Mill Inlet had the highest reading in every week. Using the site description and the background, explain the most likely reason.
  5. East Shore jumped from 3 to 12 between Week 2 and Week 3, the week after a strong west wind. Explain how the wind could cause that jump.
  6. No scum was seen at East Shore in Week 4. Should the East Shore cabins go back to drinking lake water that week? Use the data to explain.
  7. A dog owner says her dog will be fine because it only waded at the edge of the lake. Using the background, explain why dogs face a special risk.
  8. A neighbor at East Shore says she will boil lake water for coffee because boiling makes water safe. In two or three sentences, explain what you would tell her.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: Danger.
    The Week 3 reading at Mill Inlet was 22, which is 20 or more.
  2. Answer: Week 4.
    Linden Cove read 2, 5, and 8 in Weeks 1 through 3, all below 10, and 11 in Week 4, which falls in the Warning range of 10 to less than 20.
  3. Answer: Mill Inlet.
    It read 6 in Week 1, which is in the Caution range. Linden Cove and East Shore were both below 4 in Week 1.
  4. Answer: The stream entering at Mill Inlet drains farm fields and carries fertilizer and manure nutrients that feed the cyanobacteria.
    Accept answers that link nitrogen or phosphorus from the stream to faster growth at the inlet. Stronger answers note that the inlet is where the nutrient supply enters the lake first.
  5. Answer: A strong west wind pushes the floating bloom and scum toward the east side of the lake, piling it up along East Shore.
    The scum column confirms that scum was seen at East Shore in Week 3. Accept any answer that explains wind moving the surface bloom to the downwind shore.
  6. Answer: No. East Shore still read 12 in Week 4, which is in the Warning tier, so lake water must not be used for drinking or cooking.
    The toxin is dissolved in the water and can remain after the visible scum is gone, so the absence of scum is not evidence that the water is safe.
  7. Answer: Dogs drink lake water, swallow toxin when they lick scum or wet fur, and have small bodies, so even brief contact at the edge can give them a dangerous dose.
    Accept answers that mention licking fur and body size. Strong answers add that the owner should rinse the dog with clean water and call a veterinarian if it shows signs of illness.
  8. Answer: Boiling will not make the water safe, because it does not destroy microcystin and can concentrate it as water boils away; she should use bottled water or another safe source.
    Accept any response that states boiling does not remove the toxin and gives a safe alternative. A response that says boiling helps "a little" should be marked incorrect.

Differentiation

Support

Give students a tier lookup strip with the three ranges printed in large type and color-coded, and have them highlight each cell of the monitoring table in the matching color before answering items 1 through 3. For the drafting step, provide an advisory frame with labeled boxes for "Where," "How the toxin reaches you," "What to do," "When to get help," and "When this ends."

Extension

Ask students to write a one-page prevention memo to the fictional county board that ranks three ways to reduce nutrient loading into Lake Callowmere: required septic system inspections at home sale, planted buffer strips along the farm stream, and a limit on phosphorus lawn fertilizer. The memo should judge each option by how much of the nutrient supply it would likely reach, who pays, and how long it would take to show results in the lake.

ELL supports

Pre-teach "toxin," "scum," "advisory," "tier," and "shore" with a labeled sketch of the lake showing the three sites and the wind direction. Pair each audience group with a bilingual peer when possible, and allow the group advisory to include a second language version, since real advisories are often posted in more than one language. Provide sentence frames such as "Do not ___ because ___."

Extensions

Have students find their state health or environmental agency's page on harmful algal blooms and compare its advisory levels and recommended actions with the fictional Callowmere plan. Students should note one way the real guidance differs and suggest why a state might set its guidance that way.