6th Grade · Science · Activity · shared by Luke Morgan
Explore a free 6th Grade Science activity on a fish die-off mystery, where students investigate eutrophication and environmental impact.
The Mystery of Silver Lake: The Case of the Silent Shoreline
Yesterday morning, residents of the quiet community at Silver Lake woke up to a startling sight. Thousands of silver-scaled fish were floating lifelessly on the surface of the water, washed up along the northern shore. The air, usually fresh and cool, was thick with a strange, earthy smell. Local scientists have been called in to investigate why this massive "fish die-off" occurred so suddenly.
Your Mission: You are a junior environmental investigator. You must examine the evidence collected from the lake, analyze the data, and determine the exact chain of events that led to this ecological disaster. Use the clues below to solve the mystery.
Phase 1: The Evidence Log
Read the following clues carefully. Each piece of evidence provides a part of the puzzle regarding the health of Silver Lake.
Evidence ID
Source / Observation
Clue A: Water Color
The water near the surface is a thick, murky green. Water samples show a massive population explosion of microscopic organisms called cyanobacteria .
Clue B: Farm Runoff
Heavy rainstorms occurred three days ago. Large amounts of fertilizer (which contains nitrogen and phosphorus) washed from nearby cornfields into the lake.
Clue C: Dissolved Oxygen
Oxygen levels in the water were normal last week (8 mg/L). Today, the levels have dropped to 1 mg/L. Most fish need at least 4-5 mg/L to survive.
Clue D: Decomposers
Millions of dead algae cells are sinking to the bottom. Huge colonies of bacteria are found at the lake floor, "eating" the dead algae and using up oxygen in the process.
Clue E: Sunlight
The thick layer of green algae on the surface is blocking sunlight from reaching the underwater plants growing at the bottom of the lake.
Phase 2: Investigation & Analysis