ocean v. sea

71% of the Earth’s surface is covered with a continuous body of saltwater that has been divided into five sections: the Pacific, Atlantic, Indian, Southern, and Arctic Oceans.

A sea is either a part of the ocean bordering land, or a huge saline lake. Seas can be largely unbounded, like the Arabian Sea, mostly encircled by continents or islands, like the Caribbean Sea, or completely enclosed and isolated from the ocean, like the Caspian Sea. There are over 100 seas in the world.

A NASA satellite photo of the Aegean Sea.

oar v. paddle

• An oar is held in an oarlock, which acts as a fulcrum. A paddle is not captive, and can be moved freely.
• One rows with an oar, and paddles with a paddle.
• One faces backward to row, and forward to paddle.
• Oars are longer than paddles.
• Oars can be held with one or two hands. Paddles are held with two hands.
• Oars are used in pairs, and only have a blade at one end. Small craft can be propelled by a single paddle, and paddles may have blades at both ends.

Wikipedia on watercraft paddling

canoe v. kayak

A transparent foldable kayak. A canoe is a small, light, open boat that tapers to a point at both ends.

A kayak is a small, narrow boat of Eskimo design with a watertight deck with one or more openings that enclose the occupants at the waist. Kayaks are sometimes considered to be a type of canoe.

• Kayaks have a covered deck; canoes do not.
• Canoes use a single-bladed paddle; kayaks use a double-bladed paddle.
• In a canoe, the paddler either sits on a seat or kneels. In a kayak, the paddler sits within the cockpit with his legs extended forward.
• Canoes are usually wider and flatter than kayaks.
• Kayaks are generally faster, while canoes tend to be more stable.
• Kayaks sit lower in the water than canoes.

The Paddling Bares Canoe Club on canoe v. kayak

clam v. mussel v. oyster

Clams , mussels, and oysters are bivalve molluscs. Bivalves have hinged shells. Each half of the shell is known as a valve.

• Plastic boxes fashioned to look like a clam (top), oyster (left), and mussel (right). Image courtesy of Bellocchio.com. Clams have wide, round, roughly symmetrical, light to sandy brown shells. Mussel shells are long, narrow, and asymmetrical. They usually have darker blue, black, or brown coloration. While clam and mussel shells are smooth or evenly striated, oyster shells are rough and irregular. Oyster shells have one flat valve and one cupped valve.
• Clams are mobile, and can burrow in sand. Oysters & mussels are sedentary; they attach themselves to rocks or other hard surfaces.
• Different mussel and clam species live in marine and freshwater habitats. Oysters are only found in saltwater.
• Oysters are more likely to be eaten raw than clams or mussels.

Clovegarden.com on clams, oysters, mussels, and scallops

pond v. lake

Crater Lake, Oregon Because natural phenomena are continuously variable, they aren’t easily compartmentalized. Such is the difficulty in distinguishing between ponds and lakes. While virtually all limnologists agree that a pond is a natural or man-made body of standing water smaller than a lake, and a lake is an inland body of water larger and deeper than a pond, this convention lacks scientific rigor. Here are some proposed technical definitions for pond, none of which are universally accepted. In all cases, lakes would have the converse characteristic:

• A body of water no larger than 5 (or 2, or 8) hectares
• A body of water where light penetrates to the bottom
• A body of water shallow enough to support rooted plants throughout
• A body of water without wave action on the shoreline, allowing plants to grow along the shore
• A body of water that is too shallow to develop layers of water stratified by temperature
• A body of water small enough to freeze solid for part of the year

Infoplease on pond v. lake