Why are oysters safe to eat in hot summer months?

4 min readAug 29, 2021

A look at why you can eat some oysters in 100 degree weather while others will make you sick as a dog.

Oysters are my favorite food. Raw on the half shell with a slice of lemon and my local oyster bar’s cucumber mignonette, broiled with a sweet and sour sauce and served by the ocean, or roasted with a little garlic and butter, I’ll eat my fill any day of the week. I have been known to eat more than a few dozen in a single sitting, only stopping when my wallet is empty.

Here in the Pacific Northwest, oysters are a year-round delicacy thanks to plentiful local oyster farms in the Hood Canal south of Seattle. Hama Hama Oysters and Taylor Shellfish are two relatively well-known oyster farmers nearby, each shipping oysters year-round to a number of locations in the PNW and the rest of the US.

An image of my face when I get to eat my weight in oysters. (Image source: me, oyster source: Hama Hama Oyster Co.)

Every summer I make a point to order a few dozen oysters shipped directly to my front door and host a little oyster-eating party with my friends. Typically when I put in my order, it’s right smack dab in Seattle’s warmest month of August, with temperatures reaching the 70s-80s daily. The oysters ship on ice, and overnight, but I often stop to wonder why I’m able to eat oysters in my backyard when I’m unable to fish an oyster out of the ocean in the same temperatures.

Many of our public beaches and state parks are closed to shellfish collectors due to high levels of bacteria that accumulate in the water in July and August. Shellfish are sensitive to changes in temperature. As water temperatures rise, the heat induces growth of bacteria and viruses such as E. coli and Enterococci. These microbes are taken in by shellfish filtration, and can make those who consume shellfish when toxins are concentrated very, very sick. During the same months I order oysters, most oyster beaches are closed and the public is advised not to eat what they find in the water.

So why is it that farmed oysters can be eaten while wild oysters can not? The answer lies with the modern farming practices of oyster farmers.

Oyster farms typically have access to cold water


PhD in ecology and pollinator health, breaking down big ideas in science and sharing new research with all.