• All About Oceans and Seas - Answers to lots of questions like:
• Why is the ocean blue?
• Why is the ocean salty?
• What causes waves?
• What causes tides? 

El Nino: Hot Air over Hot Water - A good site from the Franklin Institute

How NASA Studies Water - For kids only -

Making Sense of the Weather: El Nino

SeaWiFS Project: The Wild Blue Wonder - Learn about the meaning of ocean color, phytoplankton, and the carbon-containing oceans

• What's It Like Where You Live? Marine Ecosystems , including shorelines, temperate oceans, and tropical oceans
• Oceans Alive!
• Planet Ocean - from Discovery Channel School
• Office of Wetlands, Oceans, and Watersheds - From the EPA
• Office of Naval Research: Oceanography

• Deep-Sea Machines - Learn about submersible vehicles that scientists use to study the deep ocean - From PBS - NOVA
• Dive and Discover: Expeditions to the Seafloor

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• Lake Pontchartrain Basin Foundation: Weekly Water Quality Report - Find out if the lake water is safe enough for swimming