Coastguard rescue teams from Felixstowe, Holbrook and a lifeboat from Harwich joined firefighters and ambulance crews to deal with a medical incident this morning.
A Maritime and Coastguard Agency spokeswoman said teams were called shortly after 5.30am to reports a person had been taken ill on a boat.
She could not specify where the incident took place but said it happened near to the western shore on the Harwich side of the river.
The lifeboat crew from Harwich were unable to get close to the boat to help because of the low tide and were stood down.
The person was helped out of the boat by fire crews and was later taken to hospital, the spokeswoman added.
Their condition is not known at this time.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here