Sylvan Lake MN: Underwater Anomaly Detected by Side-Scan Sonar After Surface Disturbance
On 27 July 2009, a witness observing Sylvan Lake in Washington County, Minnesota, from her residence spotted a nine-meter-long linear disturbance on the water surface, generating two diverging wake patterns. This was followed by a circular rotating vortex forming in the water.
The Washington County Sheriff's Department responded with a dive team, but found no submerged object at the marked position. However, a subsequent side-scan sonar survey detected an anomalous object approximately the size of a household dryer at a distance of roughly 27 meters from the originally marked location.
The case was investigated under the MUFON/BAASS framework and stands out among the 2009 AAWSAP-era cases for its instrumental detection component — the sonar return providing objective evidence of a submerged anomaly correlated with witnessed surface phenomena.
Background
In 2009, following reports of an unusual surface disturbance at Sylvan Lake in Minnesota, investigators conducted a side-scan sonar survey of the lake bottom, detecting an anomalous object or formation that did not match known natural or man-made features.
The case was documented by BAASS/AAWSAP investigators and represents one of the program's transmedium investigation cases.
The Incident
Reports emerged of an unusual surface disturbance at Sylvan Lake in Minnesota during 2009.
This prompted a detailed investigation of the area.
Investigation
Investigators used side-scan sonar to survey the lake bottom.
The sonar detected an anomalous object or formation on the lakebed.
- Did not match known natural or man-made features
- Documented by BAASS/AAWSAP investigators
Significance
This case is one of the AAWSAP program's transmedium investigation cases.
Transmedium refers to instances where UAP activity was associated with bodies of water.
The use of sonar technology reflects the program's multidisciplinary approach to documenting the phenomenon across all environments.