Seafood dining on the bay is not what it once was. Petrol spills abound, and I was paddled out to a seafood joint similar to one I'd visited years ago, and what was brought up from their live well was just a handful of dead shrimp. Cooking conditions are not real hygienic, and these folks weigh your catch when wet, then just chop it all up with a cleaver, and cook it. These restaurants are not really atmospheric, and they provide neither good value nor good quality. Stick to dining on the mainland. (Note: One floating restaurant that you can reach by a walkway from shore serves good fresh fish and seafood from clean live tanks).
The main drag of Cat Ba is chockablock with small storefront eateries. Young hostesses stand out front and try to get your attention, drag you in, and fill you up with seafood by the pound. Prices are reasonable. These places are nothing spectacular but are a good value for local seafood. Try My Ngoc. I had a meal of deep-fried squid that was positively succulent and cost less than a McDonald's Happy Meal.
Just offshore, Bien Xanh (at the north end on the way to the beaches; tel. 0313/887-529; daily 6-11pm) is Cat Ba's only quality floating restaurant. In an entirely different school from the little floating restaurants in the bay, Bien Xanh is connected to shore by a walkway and gangplanks; inside, find a fine-dining area and good fresh fish and seafood much like the town's other oceanside restaurants, but here you're in a quieter and more romantic setting.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.