If there is scum or algae visible in the water, it won't be clean enough to swim in. There are also natural hazards to outdoor waters compared with pools, especially in the summer. Blue-green algae is a type of bacteria naturally found in lake ecosystems.

Lake swimming is generally safe in 2026, but it requires a different kind of "situational awareness" than swimming in a pool or the ocean. The primary safety concerns are water quality and hidden hazards. Before jumping in, it is essential to check for local advisories regarding Harmful Algal Blooms (HABs), such as blue-green algae, which can produce toxins dangerous to humans and pets. Additionally, "Swimmer's Itch" (caused by parasites) can occur in shallow, warm water. From a physical safety standpoint, lakes often have "sudden drop-offs" and murky water that hides submerged rocks, logs, or entangling weeds. Unlike the ocean, lakes lack buoyancy-increasing salt, which can lead to faster fatigue for inexperienced swimmers. To stay safe, the "gold standard" is to swim only in designated areas with lifeguards, wear a life jacket if you are on a boat or in deep water, and avoid swallowing the water to prevent gastrointestinal illness. Always rinse off with fresh water after swimming to remove any bacteria or parasites that may be clinging to your skin, particularly in stagnant or very warm lake environments.