Good morning. Today will be mostly sunny with highs in the upper 70s. This photo of the Key Bridge was posted to DCist photos by Eric Petersen.

Mystery of the Blue Barrels: Environmentalists have concluded that white and blue plastic barrels that have been popping up in the Potomac are not from one source, the Post reports, but instead “wash down from houses, farms, and docks across the watershed.”

Pollen Levels High: With pollen levels high and expected to remain that way all week, allergy sufferers should make appropriate preparations. The Examiner reports that long transitional seasons and lush vegetation make pollen levels in the D.C. area particularly high.

Attacker Arrested: Police have said they’ve arrested the man responsible for an attack on an 83-year-old Foggy Bottom street vendor Saturday, the Post and the W. Times report. The woman has been released from the hospital and police say the man will face charges today. He was arrested after police released surveillance footage of the attack and offered a cash reward for tips.

Briefly Noted: Another fire in College Park … police arrest possible assailant of Foggy Bottom street vendor … new Southwest terminal to open at BWI …