Several lakes in Ohio as well as rivers have been placed under health advisory in the past due to high and potentially dangerous levels of bacteria and toxic algae.

Algae blooms are large formations of algae that can cover the surface of a body of water. Microcystin is a toxin produced by algae, and is harmful to humans and animals. Any concentration of microcystin greater than six parts per billion in the water results in a public health advisory. If the levels are higher than 20 ppb, the health department advises that people avoid any contact with the affected water.

Children, elderly individuals, and women who are nursing or pregnant are at particular risk from the contaminated water. People with weakened immune systems or those who are ill are also cautioned to avoid the water.

Generally, bacteria contamination prompts a lower advisory level than toxic algae contamination. Be sure that you check on the conditions before you head to these Ohio lakes or other bodies of water. No amount of fun is worth risking your health.

Below are the bodies of water that have been placed under a health advisory due to contamination. Where available, the area where the contaminated samples were pulled is listed after the name of the body of water.

1. Grand Lake St. Marys, Auglaize County - Main East, Main West, Windy Point

Algae blooms have been detected in Grand Lake St. Marys. Samples taken from the water show high levels of microcystin, which is a toxin produced by algae. Residents have been warned to avoid contact with the water. Please note that the above images were taken in 2010 during a different algae bloom event in the lake. The lake's surface sometimes appears clear. However, according to the Ohio Department of Natural Resources, both bacteria and algae levels in all tested areas of the lake vary, so you can still often consider this spot if you're looking for places to go swimming in Ohio.

Read more about Grand Lake St. Mary's State Park.

2. Lake Erie, Ottawa, Erie, Cuyahoga, and Lake counties

A yellow advisory has been issued for parts of Lake Erie due to water samples that have tested at an unsafe bacterial level. Officials have advised children, elderly individuals, and women who are pregnant or nursing to avoid swimming. Those who do swim or wade are advised to do so with caution.

Learn more about Lake Erie.

3. Little Miami River, Clermont County

Parts of Little Miami River have been placed under a health advisory due to toxic levels of bacteria. Officials are advising children, elderly individuals, and women who are pregnant or nursing to avoid swimming. Those who do swim or wade are advised to do so with caution. When things are good, it's a great beach in Ohio to visit.

Check out Little Miami River.

4. Lake Logan, Hocking County

Parts of Lake Logan have tested positively for high levels of bacterial contamination. Officials have advised children, elderly individuals, and women who are pregnant or nursing to avoid swimming. Those who do swim or wade are advised to do so with caution.

See more about Lake Logan State Park.

5. Chippewa Lake, Medina County

Chippewa Lake has been affected by a toxic algae bloom. Water samples have tested at 10.5 ppb. The lake has not been formally closed to the public, but officials have advised swimmers to exercise extreme caution and for children, elderly individuals, and women who are pregnant or nursing to avoid the water completely. Of all the lakes in Ohio, it may not be the best for swimming, but it can be excellent if the conditions are right.

Find out more about Chippewa Lake.

6. Kiser Lake, Champaign County

Levels of microcystin at Kiser lake have tested at 25 ppb, which is well above the safe limit. For this reason, residents have been advised in the past to avoid any contact with the water. Samples in the past have showed microcystin levels of 11.7 ppb.

Read more about Kiser Lake.

7. Buckeye Lake, Fairfield County - Crystal Beach

Buckeye Lake has been affected by a toxic algae bloom producing high levels of microcystin. The state has issued an elevated health advisory. Residents have previously been cautioned to avoid all contact with the water, so just be sure to check before you go to this lake in Ohio.

Learn more about Fairfield County.

Once officials pull two water samples from a body of water that test under six ppb, the health advisory on that body of water will be lifted. Algae levels and advisories fluctuate throughout the summer, so the information above is subject to change as new water samples are taken. Please follow all signs and directions at local rivers and lakes in Ohio, and stay up to date on water advisories in your area. You can visit the Ohio Department of Health website for complete details on all current advisories and for updates on the bodies of water in this list, and take a look at this video for more information on these types of advisories in general: