( CNN ) -- Tar balls believed to be from the undersea gusher in the Gulf of Mexico have reached the shores of Louisiana 's Lake Pontchartrain , a foundation that monitors the watershed reported Monday . The area affected covers a stretch of up to five miles near the city of Slidell , northeast of New Orleans , said Anne Rheams , executive director of the Lake Pontchartrain Basin Foundation . She estimated the amount of oil that has reached the lake at less than 100 barrels , with no hydrocarbon smell . `` They are about the size of a silver dollar , maybe a little bigger , kind of dispersed in long intervals . It 's not as dense as it could be , so we 're thankful for that , '' Rheams said . Cleanup crews had collected more than a half-ton of the tar balls -- 1,020 pounds -- by Monday evening , and the oil will be tested to confirm it came from the undersea well that has been spewing into the Gulf since April , the Joint Information Center in Houma said Monday night . But Rheams told CNN , `` They 've got to be from the spill . '' Tar balls had previously been spotted in Rigolets Pass , which connects the lake with Mississippi Sound . Officials in Orleans and St. Tammany parishes have been using heavy booms , barges and skimmers to defend Pontchartrain since the early days of the disaster , but Rheams said high waves and strong easterly and southeasterly winds have complicated the effort . `` The main thing is that they are an indicator that it could be coming more so this way , '' she said . State officials have closed a swath of the southern part of the 630-square-mile lake to fishing following the discovery , but there was no sign of impact to wildlife as of Monday , Rheams said . The Coast Guard reported Sunday that a shift in weather patterns could send more oil toward sensitive shores in Mississippi and Louisiana , and bad weather over the past few days has significantly hampered cleanup efforts . Rheams said that pattern was expected to persist for at least three more days . Federal officials have estimated that between 35,000 and 60,000 barrels ( 1.5 million to 2.5 million gallons ) of oil have been spewing into the Gulf daily since April 20 , when the drilling rig Deepwater Horizon exploded and sank in about 40 miles off the Louisiana coast . Efforts to plug the gusher have so far failed , and oil from the spill has been reported as far east as the central Florida Panhandle .
Hot , weathered oil in Lake Pontchartrain . Tar balls described as ` ` about the size of a silver dollar '' Part of Mississippi closed to fishing . High waves , strong winds preventing navigation .