The canals are filled with dangers. You'll encounter Combine soldiers on foot, turrets, and even Combine Gunships. When facing Gunships, aim for their weak points (usually the glowing parts) and keep moving to avoid their heavy fire. You'll also need to navigate through various obstacles, including collapsed bridges, explosive traps, and toxic waste. Sometimes you'll need to dismount the hovercraft to clear a path or solve a simple puzzle. Look for health and suit power recharges along the way. You'll eventually reach a large dam where you'll need to clear a path to continue.
Half-Life 2
Canal Navigation & Combat — Half-Life 2 Guide
Master Half-Life 2's canal navigation and combat. Defeat Combine Gunships, bypass traps, and reach the dam using your airboat.